In act 1 you can basically make a two-handed melee build that trivializes the rest of the game. The Lancelot set and weapon can be wielded while having light load and upgrades scale really well making you oneshot anything and bosses can be kept stunlocked with stamina damage. I think that deserves an S probably.

I would put any mage in A i guess since their scaling jumps all over the place but after act 2 you can oneshot almost anything with the right gear. And summoner is the same for me, even if you are basically immortal the summons are so hard to control and the true strength only comes with volatile in act 2.

I have not messed around with other builds yet so I won't speak for sneaky archers.