I haven't seen any reason to criticize Grubb. I don't find myself questioning the playcalls. Players seem to know their assignments and situation.
The offensive issues are mostly because of the line. They are inconsistent. Plays are getting blown up immediately, passes are getting batted down, and when Geno gets rattled he likes to throw interceptions. We don't have a good enough QB to mitigate a bad offensive line. That isn't on the coordinator.
You could argue that we should call plays that don't rely on the offensive line, but we already do that and we can't just always call quick throws to the sidelines or running plays. You gotta make attempts downfield. The line has shown that at time they can actually generate a really nice pocket.