Graves is too damaging, for how tanky he is

All's a matter of perspective. It's ok to have a ranged bruiser in League that isn't intended to poke (Jayce) or turn into a teamfigthing AoE CC tank (Gnar). It's not ok for him to not have the normal counterplay of "if fails at kiting, gets outstatted by melee". Sure, you can consider that the issue is with his tankiness. Or you could realise that he shouldn't with the same build as a melee do so much more damage in melee range due to his autoattacks stacking up.

His passive should probably cap in number of possible single-target bullets against champions.