I think I understand now why Riot makes some champions stronger than others for periods of time.
Making a champion Rengar really strong usually causes players to play Rengar a lot. Since no champion is without their counters, making one or a few champions very dominant also makes their counters strong and popular. So since rengar is strong right now that means champions like zilean and kayle may also be popular to deal with his single target burst damage or champions like tf who can reveal him from stealth.
You vewy sneaky, Riot. youa vewy sneaky, indeed O.O
This actually drastically changes my opinion of the game. I have been thinking lately that you guys are just being really lazy and stubborn about not balancing champions but I get it now :D time to go practice my kayle, zilean and tahm kench.