Stop smurfing/toxicity -> Make it so you /have/ to buy champs with IP rather than RP
To be eligible for Ranked. And maybe up the number of champs you need to be able to head into Ranked. That way, people actually have to play normals for at least 70 games (buying all the 450 champs = 11 champs = 4950 IP...assuming it's around 70 a game, that means ~70 games).
Or as well, you can also make it so people have to play x amount of classic games at level 30 only. (100+?). Level 1-29 aren't justifiable as 'games played' because they're stupid easy. I haven't smurfed, but I recall playing with a low level friend (cause she was new and wanted to learn) and the games were laughable.
As well, since people would have this kind of 'training', they might be less bad/toxic/??? when they finally get to ranked. Ergo elo hell would die off, ergo less people in bronze without capacity to get out with trollish and/or afking teams.
Haven't played Ranked recently, I'm just going off what I remember.