Unbalanced champions perpetuates unbalanced champions
Make a champion weak, hes not seen in the game often, when he is, teammates don't know what to do with it, making the champion lose more than he otherwise would have.
Having some champions picked 10 or 20 percent of the time compared to less than 1% is grossly unfair to the game and to players.
Riot can't seem to understand the fundamental reason swhy some champions are persistently annoying or broken or OP. To do so they would have to own up to huge fundamental flaws in games design and distribution of power and CC and mobility in abilies of champions.
Its okay Riot, keep putting bandages on a gaping oozing wound, making the game more convoluted as the years roll on. I'm sure it will magically all work out someday.