From what I know of Grim, yes - he would do better if his role allowed him to take more space and play aggressively, like EliGE, but can't since EliGE is on the team.
Still, Stewie leaving could open up some space for Grim to take, and he could ditch some of the tough/supportive spots for someone like RUSH or VINI who don't have as much mechanical skill but are disciplined players with minimal ego.
RUSH would be a big benefit for the team's mental stability. He can handle most roles decently, and he's mature enough to handle big egos. Honestly he'd be a great coach in the future, but his skill isn't gone yet.