I do think the combination of high armor, HP and the ability to lob shells over shot blockers might prove problematic. It can deal damage from safety and will be very hard to kill. Brummbär is already (borderline) OP because of similar traits but that one at least has a low HP pool to balance things out a bit.
I advise you to watch 2v2 tournament games from the weekend.
KV-2 was used, but wasn't overwhelming as you claim.
Brummbar wipes stuff easily, KV-2 didn't in any mode.