Overall a very good post. I do have a question about the feat comparison, though. I had thought that one of the big complaints about 4e was that it had a lot of feats that didn't do a whole lot in comparison to 3e. 5e on the other hand has feats that do at least as much as 3e feats and often more. I never played 4e really, so I don't know from personal experience. Were 4e feats similar to 5e's in strength?
They tended to vary, and I freely admit that
some were weak. Many, however, were quite good, and not just because they were "tax feats." For example, later in 4e's life, they started adding more flavorful/interesting versions of the infamous Expertise feats, that would encourage players toward certain behaviors (e.g. Devout Protector Expertise was clearly for Paladins and Clerics: +1 per tier to hit with one-handed weapons and holy symbol implements. But it
also gave your allies a +1 shield bonus to AC if you were using a shield--a super nice benefit for many allies that wouldn't normally use a shield.)
Basically, if you stuck to the best 20% of feats or so, they tended to be
really really good. The worst 20% were probably more like 3e feats, but even then, actual outright stinkers (like 3.x Toughness or Pathfinder feats like Death or Glory, or the original version of Prone Shooter which did
literally nothing) were quite rare in 4e.
5e, in making feats compete with stats, has generally beefed them up...but it still has a few feats I would call "not worth it" and others I would cal "near-mandatory." Elven Accuracy for anyone who qualifies, for example, or Elemental Adept for anyone doing a lot of elemental damage (e.g. Gold/Red Dragon Sorcerers, Evoker Wizards, Wildfire druids, etc.) are near-mandatory, while several feats in the PHB come across as "permission to roleplay" rather than feats with any bite (e.g. Keen Mind, Tavern Brawler), provide vanishingly small utility for the cost (Savage Attacker, Weapon Master), or
If you account for the fact that a 4e character would get 18 feats (19 if human) whereas the
absolute maximum a 5e character can have is 8 (any race with Tasha's in play, playing a Fighter) and most will only get two or three at best IF they get to high level, some of the "smallness" of 4e feats can be forgiven--just as you'd compress 30 levels of 4e into 20 levels of 5e, you'd compress those 18 feats down a LOT since they weren't competing with ability score increases. If you treat every 5e feat as being (roughly) the equivalent of 2-3 4e feats, I think things come out pretty well--especially because ideas like 4e's multiclass feats are fairly clearly reflected in things like Metamagic Adept, Eldritch Adept, Martial Adept, etc.
Edit: I guess you could TL;DR this by saying, "4e is pretty clearly a midpoint between 3e feats and 5e feats. 3e feats are often INCREDIBLY boring, and you may need to take half a dozen of them just to unlock the one special feat you want. 4e usually avoided feat-trees, and while it had some boring feats, the feats most people would
want to take were solid, chunky, and reasonably potent. 5e doubled down on this, and then doubled down
again by making feats compete with ASIs, so its feats absolutely had to be really good.....even though some of them still aren't."
5e feats are probably 60% to 80% good options, with roughly a quarter of the good options being "you're taking this unless your DM forbids feats--possibly even before you max out your main stat." 4e feats aren't as big, nor quite as
consistently good, but you can clearly see 5e iterating on 4e's design vis-a-vis 3e's design. 4e clearly had the stronger influence.