Originally Posted by
Ignimortis
That's also a part why I can never really "switch". 5e doesn't give you enough resources (or choices, or character build points - call them whatever you like).
This right here is basically no resources invested into attack besides ability score increases. You didn't buy a magic weapon, you didn't spend any feats optimizing to-hit, you've got a really mediocre starting STR score - all in all, this is a barebones character. There are tons of things you can do to make missing impossible except on a 1. There are tons of things you can do to get your damage in triple digits instead of 11-22. You've invested maybe 1/6th of your resources into attacking and still have a good chance to hit and do some damage - not a spectacular amount, but still.
If magic items are off the table for both cases...a level 20 Barbarian had 5 ASIs. Let's assume they're distributed as usual and that the barbarian started with 16 STR, as they often do. So that means 2 ASIs for +2 to STR, one for GWM, one to Fell Handed or Sword Mastery for +1 to-hit, and another one whenever, because I'm not sure what else can be done, which makes the 20 level increase pump him to 24 ST. The barbarian is at 6 (proficiency)+7 (STR)+1 (feat)=14 to-hit without a magic weapon. He can give himself advantage through Rage, sure. But the typical CR20 monster has 20 AC, so the barb misses on 5 or less, and if he uses GWM for damage, on 10 or less.
That's worse chances that a barebones 3.5 barbarian on a subpar chassis. And if his axe is non-magical, then he loses half the damage. He performs about the same as the 3.5 barb in the same conditions, but the 5e barb has invested 4/5 of his resources into attacking well, and the 3.5e barb has barely spent 1/6th. Add magic items and other resources into the mix, and the 3.5 barb comes ahead, because he can't miss on anything but a nat 1, and he does enough damage on his round to absolutely wreck the monster's day, and DR rarely even comes up.