As I said very situational. AP Kog's laning is sub optimal until you have tear, the mana useage is hard to go through. He struggles alot until 6 as you said unless it's against someone like Malphite where he can sit behind minions and auto with ooze to make Malphite's life miserable. Varus mid is normally a manamune into penitration station. TL;DR Don't play Kog mid against any champion that can push him hard