Whilst I do agree, if he's decent his impact on the team will be far greater than his ability alone.
Because we have nobody who can really play that position as it stands, merely having somebody there who can actually play there should be a huge boost based on tactics alone.
Think of it as if we were playing with no goalkeeper. The impact of then playing any goalkeeper, even if they were shit, would be huge.
Yeah you're right. Just having that presence and option in the team that we don't currently have should make a big difference, and I guess if teams do single him out for special treatment, it creates more space for other players to play and less emphasis on Benteke, so the team as a whole will benefit.