So, to start: Spaghetti posting is explicitly against SV's rules. Setting that aside, however:
The relevant issue is 'making it hard for casual readers to understand, thus disrupting the proper running of the thread'. Since this is a Megathread, it shouldn't be a problem if we're careful.
Tanking is a two-part thing: Part the first is being able to take being attacked, and a number of classes in D&D can manage that. On its own, this is called being tough, or being sturdy, or not being made of glass.
It is not, however, Tanking without the second part: Forcing enemies to focus on the Tank, rather than the squishy non-tanks. In MMOs that include Tanking, this is done by hard mechanics.
In D&D 5th, there are... A few spells, I think, and class abilities, mostly in the hands of the Paladin. For the most part, however, you're limited to roleplaying, and cannot mechanically force enemies to target the character most capable of handling their attacks.
Opportunity attacks, for a start. The Polearm Master and Sentinel feats, especially the latter. Booming Blade, the War Caster feat, or both. I'm pretty sure I've seen a Barbarian subclass that can move as a reaction in order to chase enemies, but it might've been homebrew.
Oddly enough, the Rogue is probably a very good tank if you can make them tough enough to survive it. A Barbarian dip is
great for that.
Any tough Grappler can make a viable tank.
Heck, you can even just play a gish and take lockdown spells!
Those are
all viable methods for forcing opponents to focus on your tank, and that's leaving aside the support spells (Wizards have a lot) designed to provide lockdown for tanks who can't do it themselves.
Passive powers are only interesting when they're used. Having a Phylactery, for example, only comes up when one is using it to refuse to die. Further, that's an NPC ability, and thus derives most of its interesting elements from the players doing things to break it.
Phylactery may be a bad example, because it's probably more fun to abuse your resurrective immortality than it is to go to ridiculous measures to guard your heart, at least most of the time. I'll try to rephrase.
Active powers, like most attacks and skills and so forth, are interesting for what they let you do.
Limitations, such as 'nearly perfect' defenses, are interesting for what they make you
avoid.
Since passive defenses are rarely interesting, and the Wondrous Items chapter talks up magic items as being wondrous and awesome and special, I want magic defenses to be powerful but with interesting flaws. It's a very old trope for a reason.
Now, setting aside the basic concept itself, what on any plane are you talking about regarding Fighter? Avoidance tank? Where in the seven hells are you pulling that from? The only survivability feature the core class has is Second Wind, a once per rest recovery ability.
Their AC is some of the best in the game. Between the bonus feats (for defensive feats and stat maxing), their full armor proficiency, and their Fighting Style options, Fighters can be
quite difficult to hit, and they get Indomitable for saves. That's also before considering subclass features.
The standard assumption in D&D is that magical items are good, and do not hurt you. Cursed items are the exception, and most players will avoid them if non-cursed items are avalable, regardless of the bonuses.
I think it's doable with some balancing. People do seem willing to wear Heavy Armor despite the disadvantages.
Do I need to go dig up my long effort post about why the MMO comparison for 4e is wrong? I can.
I'm curious what people think the best D&D video/computer games were. Anyone?
I've heard 4E is actually a very close comparison for
Overwatch.