Quartz
Hero
You're assuming a 20th level fighter wouldn't have magical plate and shield. +3 is the highest that's been hinted at (as legendary items). A level 20 PC probably has run across those at some point. So that 20th level figher would have AC 26.
But then you could give the barbarian a Shield +3 for an AC of 27. And as in 3E the fighter is still dependent upon magic gear. And the fighter has Disadvantage on Stealth checks.
Nah, you were sort of right; the berserker subclass can "frenzy" for an extra attack each round (as a bonus attack) while raging, but that makes them take a level of exhaustion, so you have to be careful with it.
Ah right.
Also, remember that a lot of people won't have maxed Dex, Strength AND Con even by level 20;
I agree, but ISTM that a barbarian going for L20 would max Con and Dex over Str. If you end up with Str 22 instead of Str 24, that's still badass. If you end up with Dex 18 instead of Dex 20, that's only a loss of 1 point of AC and still badass.
there are quite a few feats you can take that are probably worth more than a bump to your AC and dex saves. For example, let's say you use three feat slots to go from 16 to 20 Dex and 18 to 20 Con; you could instead take +1 dex/+1 con, then Resilient (dex), then Durable, and you'd end up with the same Con, more hp, and much better Dex saves, and only one less AC.
I haven't analysed the feats particularly thoroughly yet.