Actually a CF creating goals out of nowhere is a damn good sign. It's the indication of he can work on his own when supply dry up.
But either way, yes, there will be ups and downs as with any striker.
It actually paints a grim picture. Comparing an attacking possession based team vs a team that sits back and counter on opportunity. Latter should concede less than the former.
For a player of his calibre, at times he should have been closer to the action in final third. But you don't see him much there, and probably rightly so because I don't think he has a pace to track back quickly and we need him in center midfield...