What counters a tank in the early to mid game?

I know that ADCs beat tanks in the late game, but that's because they have a lot of items that scale well late. So who exactly beats a tank in the early game and mid game? Your first midgame teamfight or two are important to setting the tone of the rest of the match. However, a number of ADCs are kind of weak come mid game which is why they are getting rageblade to compensate, they are trading in late game potential for mid-game relevancy. Tanks aren't really bothered by assassins in the mid game. AP champs aren't particularly great at shredding tanks. ADCs don't have their items yet. Tank items are also kind of cost efficient and cheap... you don't see tanks paying 3600gp for their first core item.

So when mid game comes around, what beats a tank?

+ doesn't count because most people don't have enough games under their belt to play vayne effectively and frankly your typical solo Q player isn't coordinated enough to think about picking a protect the vayne comp or pulling it off perfectly.