Realism depends on you and your Storyteller (the person running the game). As for which is more deadly it's kind of a tossup and in both cases can have a lot to do with relative power levels. For example, an oWoD Lasombra Vampire with enough experience and low enough generation can sprout a bunch of shadow tentacles and then pick you up so you can't escape and beat you to death with the rest from across the room. Likewise an oWoD Tremere Vampire with enough experience could split their mind in two, telekinesis you into the air so you can't escape, then use the other half of their mind to blast you with fireballs until you're dead. (These are pre Vampire the Masquerade 5E examples.)
By comparison, in nWoD a Werewolf can attack you, deal some damage to you, take a bunch back in turn, and as long as the damage they took isn't aggravated they can come back in a couple hours at most ready for round two. 1st Edition nWoD Mage has a rather notorious example, once posted on the internet that I've since lost links to, allowing you by RAW conjure up a football field's worth of (again iirc) chlorine trifluoride to be dumped on someone from the other side of the planet. Or technically anywhere in space. You could be on Pluto and drop it on them when they're on Earth.
Basically the higher you go, the more deadly things can become.
Depends on how much experience you've got. At base character gen you're basically a mortal with some tricks, though those tricks can be quite good. But put in enough time and effort and you'll definitely feel powerful.
One. They need to be good and prepare but someone hitting you from a well prepared position with a barrett 50 cal with knowledge of what to hit you with or how to hit you can end you in an instant.
For just regular average people in nWoD that's probably a dice pool of 4 (attribute+skill, Human Average for Attribute and Professional level skill)
This then comes down somewhat to luck, so we'll say average of 1.5 successes per person rolling plus 1.5 damage per roller (as pistols are either 1 or 2 damage). So that's 3 damage per attacker. For vampires that's 3 bashing damage per attacker. For Mages, Werewolves, and Changelings it's 3 lethal damage. "Average" health is 7, 5 for size factor and 2 for stamina.
Changelings are likely the first to drop as they don't have healing powers quite on par with the big 3 (Vampire, Werewolf, Mage). But as long as they can get some kind of 'threshold' they can open a portal into the hedge to escape. Assuming there's no escape, you're looking at 2-3 (luck variance for some random attack hitting the +1 damage needed) attackers all hitting before the Changeling is unconscious and bleeding out (assuming no body armor). (Others who know more about 2E or who want to bring up something I'm forgetting about 1E feel free to chime in and correct me.)
A Mage is likely to be a bit more difficult, though how much so depends a lot on the Mage's powers. A Mage is incredibly likely to have some form of Mage Armor as of 2E Awakening where Mage Armor is something you get just by getting to 2 dots in the appropriate Arcana, so lets go through each Arcana's Armor. Death will let the mage take damage more easily as it downgrades a number of lethal from kinetic attacks to bashing equal to their dots in Death. Fate adds their Fate to their defense and allows that defense to count against Firearm attacks. Forces applies Forces dots as general armor (which is to say, Forces Dots as Armor against all attacks). Life gives you half your Life Dots as both General Armor and as a bonus to your Defense which is now calculated with the higher of your Wits or Dexterity. Matter gives you your Matter dots in general armor against all physical attacks and this armor is immune to armor piercing. Mind adds your Mind dots to your defense. Space lets you add your Space dots to your defense for attacks you're aware of, lets you apply your defense to firearms attacks, and if they miss you can spend mana to redirect the shot to another applicable target with successes equal to you Space dots. Spirit downgrades a number of points of damage from kinetic attacks from lethal to bashing equal to dots in Spirit (same as Death). Time adds your Time dots to your Defense and lets you apply you defense to firearms attacks. Prime gets you nothing.
These are all before the Mage starts slinging spells.
If we assume just the 2 dots and that there are enough attackers to shoot them down before they can react then you have 4 categories of +Defense on Firearms, +Armor, Death & Spirit, and Life.
+Defense Mages with the default 2 Average human means that the starting attack pool of 4 is now down to 2 dice without any training in Athletics. This significantly increases the necessary amount of attackers necessary for an overwhelming alpha strike. Because I'm lazy, we'll literally just half the success average down to .75 and assume that all Mages being attacked are anemic nerds who sit around playing RPGs literally all day long.

Now we get 1.5 successes every 2 attackers, meaning we're immediately doubling the number needed to take down the changeling from 2-3 up to 4-6. (Again, I'm being incredibly lazy in calculating this.)
+Armor Mages don't get their Defense, so we're back up to the 4 dice pool, but now that 3 damage per attack is down to 1 thanks to the 2 points of General Armor. Meaning, again by lazyogic calculations, you need 7 to drop the Mage.
Life Mages don't get to apply their defense to firearms, so they only get 1 armor instead of 2. Meaning attacks hit with 2 meaning you need 3-4 attackers to drop the Life Mage.
Death and Spirit Mages downgrade the first 2 damage they're hit with into bashing, which just pushes it to a confirmed 3 minimum to drop the Mage (as this downgrade mostly has the effect of giving them what amounts to 2 additional health levels).
Now moving onto Werewolves. The toughest killing part for a werewolf is when they go to Gauru, so we'll just start there (lazyogics). First, we're now up to 11 Health levels (+2 stamina and +2 size). Second they get defense on Firearms attacks now. Third Lunacy kicks in so every attacker might flip out and run off screaming into the night, but chances are lower the more people are all there together to gun down the monster. As such due to lazyogics we will ignore Lunacy and assume there's a large mob and as such any screaming runners are just easily replaced with people hardened enough to not run. So going back to the dice pool of 4 the Werewolf has full defense on firearms attacks and their defense is now 3 minimum (assuming average 2 Wits and Dex). Oh my. We'll invoke lazyogic calculations again so now the .75 is halved to roughly .3 which in turn means that we're now getting 3 damage roughly every 4 attackers. Given that the werewolf is likely going to death rage and likely stay conscious to keep murderizing the attackers we're looking at 32 attackers to 100% drop the Werewolf.
Now Vampires, who are somewhat more complicated again due to discipline variety. Celerity can be used as Defense against firearms attacks and can let them just reflexively act before you all can so they can attack or run, Resilience gives its rating as additional Stamina and can then be invoked to just ignore incoming damage (Resilience+1 for each invocation). This is before we get into devotions (example, Body of Will lets you invoke Resilience for free for a number of rounds equal to your successes on Body of Will's activation roll, meaning ignoring incoming damage as though you had general armor equal to Resilience+1). If we assume none of this then we're back to 1.5+1.5 for 3 damage per attacker with a total of 5 attackers minimum to take down a vampire by pumping them full of bullets until they fall into Torpor.
Note That both Vampires and Werewolves of higher power stat (Blood Potency for Vampires and Primal Urge for Werewolves will mean they can spend their energy to heal more damage and therefore increase the number of attackers needed). Also note that I've completely skipped out on how each attack degrades your Defense by 1 due to Lazyogics and the fact that many of these supernatural beings are going to have things to help counter attacks somewhat. As such it feels like a decent trade off from my perspective to ignore degrading defense in return for ignoring that the Mage might be able to banish all the attackers to the Shadow Realm, or how the Changeling could trick many to following them through a door into the hedge to die, etc.
In general supernaturals range from 'maybe slightly less squishy then normal people due to some supernatural tricks' to 'omg we literally can't shoot the mage, and every time we try one of us gets hit instead!'
Also again, if anyone isn't nearly as lazy and tired as I am they're more then welcome to do the actual math on all of the above, or to correct me where I'm wrong or forgot something so long as it's not to correct me about things I've specifically Lazyogiced.