It's called resource management, learn to trade and farm using mana efficiently. As far as Zhonya's goes... that's one of the most powerful items in the game.
I think the game's in a pretty good spot at the moment. The only champs I perma-ban are Fizz and Zed. Two of the safest champs in the game as well as high amounts of damage is a little over powered imo and annoying to go against at the very least. I'm certain the Zed ultimate shadow change a while back was ultimately a buff. (Safe getaway)
But yes, as a top main I'm pretty happy with how the game state is. I'll continue to play this game no matter what changes they make, I'll just adapt.