I don't know about other ruins, but Denandsor had (before the potentially enemy NPC recently it in our campaign) reasons for staying untouched those 700 or so years (or at least the reason was working until all 300 Solars returned to the world).
Yes, it had a big plot sticker on it saying "SOLARS ONLY, EVERYONE ELSE FUCK OFF BECAUSE PLOT", with a secondary sticker saying "no, mental defences and other package deals of being an Exalt don't work against this, what do you mean "if it's so easy to deny the Exalted the ability to enter an area, why didn't the Primordials just set up massive areas of 'your Dragonblooded army can't enter here' during the War?".
Anything that artificially segregates off a parcel of the setting as only being allowed for speshul snowflakes by gating it behind a You Must Be This High To Play No Takebacks Or Loopholes rule is not very good writing, especially when it's as poorly justified as Denasdor is ("something something Artifact something fear aura you're not allowed unless you're a Solar go away what do you mean why hasn't the Artifact shut down after two thousand years with no maintenance or refuelling; shut up, you're spoiling the special Solar playground").
To go into more detail on your comparisons, though. Firstly, the word "medieval" is very imprecise, and covers a range from about the 5th to the 15th centuries. Despite people
thinking that it's all one homogeneous period, that's literally
a thousand years, which is a timespan that does the equivalent of lumping the Battle of Hastings in with the First World War. I'll assume you're talking about pre-Industrial times and average it out at about the 10th century.
The fantasy commoner is uneducated and probably not very smart (in fact quite the opposite), but can surprise the hero with a few useful bits of SimpleMindedWisdom, and perhaps knows a secret folk recipe or two. The NFAWMH commoner's most coveted secret wisdom is probably Yet Another Way to flavour the alcohol s/he brews in spare time.
"Commoner" is another really poor description that shows very little understanding of the dynamics of the time. You didn't use "slave", though, so they're presumably not serfs or other un-free workers of the kind used at the time, which means they're probably part of quite a complex feudal system. If they're a farmer, they may well use slave labour themselves on their fields, and know a fair bit about crop rotation and wind or watermill industry, which they use for grinding flour and other rote mechanical labour tasks. They don't own the land they work, but they cultivate it and pay rent to a landlord, who can't go too overboard in treading on them because he depends on them to produce his crops for him. Further, "uneducated" doesn't mean "stupid" - people are people, who obey normal distributions no matter what time period they're born in, and to ladle cliched tropes onto what may well be a bright or gifted boy or girl born into a lower class family is to ignore the fact that bright and gifted kids have been being born in every level of society since humans evolved.
And such people do not passively stay put and content themselves with "simple-minded commoner folk wisdom". They work, they strive, they test and push and
break boundaries in order to get what they want. They always have and they always will. That's where stories are born. Dismissing both sets as "commoners who aren't very smart" is
exactly ES's point about stripping away human agency. What about the commoners who fake being nobles to try and get a leg up in the world? What about the ones who ferment rebellion, or trade chores so they can be cleaning near where their lord's son is having lessons from private tutors and so steal an education from overheard scraps? What about the thousand and one different ways that
people - not video-game NPCs - will always act like people, with goals and aspirations and drives of their own, and refuse to stay in little trope-named boxes?
The fantasy assassin kills the target with an exotic poison from an interesting ambush. The NFAWMH assassin spends the front payment to hire a bunch of thugs and storm the target at the evening dinner at the local tavern.
Your early 10th-12th century assassins probably acted like the predecessors to Japanese
shinobi or like the Arabic
fidaiyn, staking out a target for weeks, months or even years, using disguise and nerve to go under cover as a servant, and then using poison, a concealed weapon or a garotte to kill an unaware target. A fancy exotic poison is easily traceable, so a competent assassin uses surrounding tools in clever ways, and if at all possible tries to set things up to look like an accident unless they're making a deliberate point. They're an early form of asymmetric war who use the exact same principles that modern terrorists use, and who can be used to draw parallels to them in both tactics and psychological repercussions. They're heavily tied into the political arena, since most of their work will be in relation to it.
The (non-mortal) fantasy hero-to-become-empress is a paragon of mental acumen, drive and personal power, enforcing her will upon an ancient artifact of doom in a feat of ancient heroism. The NFAWMH 'god-empress' is largely a figure who just happened to be lucky to fit the criteria the artifact considered acceptable, or even a person claiming the title of someone long dead and brainwashed into fitting the artifact's criteria.
Honestly, I don't even need to address this one, because the latter is just as cool as the former - that's what the Exalted are, after all. Someone who got lucky enough to get a superweapon that they didn't "earn" or "deserve", and now they have to figure out what to do with it. That's a story in and of itself, to say nothing of how they got their hands on the artifact or where they found it, since - as ES said - most artifacts that are just lying around where a little effort can get at them were got at several centuries ago by opportunists.
The fantasy knight is chivalrous if perhaps a bit too uptight; he was likely knighted for some feat of heroism; he also probably sacrifices extra wealth to the temple of his faith if he's got a slight paladinish vibe. The NFAWMH knight is a bandit with a noble title bought with stolen gold, keeps robbing everyone on the road while paying lip service to the local christianesque temple because the temple is corrupt and will use its connections to protect the knight against repercussions from those higher up on the social ladder (and probably wastes the rest at the local tavern on booze).
Knights as we think of them - shining armour on horseback - are actually fairly late into the medieval ages. A knight (though Exalted
strenuously avoids even the
word 'knight', as part of its "no, we're not DnD" thing) is a noble lord who is an integral part of the feudal system. He's a military officer and a member of the lower nobility who has been trained from the age of seven, if not younger, and who is basically an elite special forces commando in terms of the money and time that went into training him. He's often more than just a mounted elite soldier, and in fact has a responsibility to raise and maintain troops for his monarch or lord, which are a foundational part of the feudal system, wherein the power of the Crown comes from the nobles who it grants land to, who support it with their regiments. Any view of the king being the ultimate power is flawed, because their power comes from the nobles, and thus they can't anger them - much like how the modern government has to play nice with big-money companies who control much of the economy, and who can apply considerable muscle to any discussions of law or policy. Are you seeing a pattern here of parallels to the modern world seen through the lens of the old ones, and economic and political reasons behind things? It's a much more interesting one than Generic Fantasy World where none of the actual underpinnings of society are present, and real-life stuff like this is just excluded completely.
The fantasy pirate has a ruthless but strict code of honour, lives the pirate life for the sake of the wind and the constant travel and the thrill of battle and chase, and will ransom caught nobles for outrageous sums. The NFAWMH pirate is a Somalialesque commoner living the pirate life largely out of necessity, during raids is almost as scared as his victims, and probably killed a dozen unarmed civilians out of fear of dealing with the problems of keeping a hostage unharmed.
Piracy is an outgrowth of insufficient government - read
The Birth of the West, by Paul Collins, which goes into detail about how the modern West emerged from 10th century Europe. In short, piracy is tied up with raiders, and is a constant threat in this timeframe. Magyars in the south, Saracens in the west and Vikings in the north were all constant facts of life who sacked towns, plundered monasteries, and generally terrorized their victims. In some places, the rulers fought back - some successfully, some not. Other places just paid them off. All of them
happened, however, because of places where there were no strong central powers or rulers - isolated societies that were unable to defend themselves against predation. Somalia is a perfect example of this; a haven for pirates where there's no law or central authority - so if your fantasy world has pirates;
where are they coming from, what caused the collapse of authority that gave them a foothold on the region and who's trying to do something about it (and what)?
A fantasy crime lord will weave elaborate schemes, be the leader of a Thieves' Guild, and if he's evil enough, will even kill his opponents in a magnificent display of power and of being to reach anyone (not necessarily personally, but e.g. by the assassin from the begining of the list), striking the fear into the citizens of the region. The NFAWMH crime lord is the local baron's embezzling petty accountant.
Insofar as crime lords exist, they're the ones who weld together crime on a bigger scale than pickpocketing. There won't be a "thieves's guild" where all cutpurses and pickpockets pay a fair share of their earnings to the Common King; the "crime lord" will be the one who
organises and uses planning and infrastructure to go after
big targets. Kidnappings and ransoms, protection money, loan sharking, gambling, drug trades. Look at the
yakuza, look at the
mafiya; look at the societal pressures that give birth to them and the way they do business. Look at how they recruit members, how they
keep members and how they enforce loyalty. Look at the way that they're
infrastructural; they're not built on fantastical notions of thieves all breaking one set of laws but obeying their thief laws for Plot Reasons, they're rooted in cold hard profit and psychology - and are a lot harder to take down than just beating up the King of Thieves.
The fantasy pickpocket kid, when caught, will tell nasty-but-hope-filled hard luck story, and probably have a HeartOfGold. A NFAWMH pickpocket kid will more likely have a feral-ish mentality and/or too far gone due to the locale/period's equivalent to sniffing glue.
If you've got kids on the streets resorting to crime for a living, that gives a raft of stories. Look at Victorian London for what happens here - such kids can often get
really inventive in what they do to survive, and again, stories are born there. A lot of them will die, yes, and that tells you something about the culture and the class warfare in it (oh hey, more parallels to modern classism and poverty, whee~). And the reactions of those around them and who among the higher classes try to help and do charitable work will tell you more.
Standard fantasy is
boring. It presents the veneer of a society, but it ignores how actual societies in the time periods it lazily takes aesthetics from actually worked, and is often wilfully blind to some of the things that existed alongside what it uses - like how cannons were around in Europe from at least the 13th century and handheld firearms were around a couple of centuries later; at the same time as the stereotypical image of the mounted knight. It ignores the economic and political and societal reasons for things that happen, and it strips minor characters and entire groups of agency, assuming that commoners (bar a few Special Snowflake heroes) will be content to stay commoners and the like; boiling them down to a few groups of cliches and trope-block LEGO. One of the promises that made Exalted so inviting and original was that it would sweep all that away and look cynically and hard and
accurately at realistic mechanisms of how human cultures worked, and then merely add magic on top. That's far more interesting, to me, than repeating the tired cliches of Generic Western Fantasy - or alternately of repeating them and then adding a layer of dirt and rape on top, as in ASOIAF.
