Let’s start with a Rogue.
The legendary aspect that gives the Flurry 360 degrees attack doesn’t seem to work right. I seems to miss the enemies behind the character or just deal a lot less damage to them. I haven’t test it and I might have just read how it supposed to work wrong.
Barbarian absolutely need at least one basic skill that hits multiple enemies. Something like a Cleave in D3 or Paladin Zeal in D2.
Even a Sorcerer has that electric whip when Barbarian has to kill ten ghouls or vampire bats one at a time while tanking the hits from the rest of them.
Make Frenzy hit multiple targets in a sequence like Zeal or Flay hit enemies in an arc like Cleave. Generating enough Fury to use better skill is a slog.