For me, it's the overt power that 5e characters have. It was insane at how easily a problem could be solved by a class feature (other then fighter cause fuck you).

Bards, most of their spells will help in some way shape or form.

However, I've had a wizard and a paladin in a party at mid level and the paladin was the one that constantly had a silver bullet for any given adventure.

But it's really just best to look at a given class / subclass and look at what kind of utility they provide wholistically (abilities, etc). Because you won't beat a wizard at casting spells. It's the whole point of the class.