I can see this whole "less XP to get to level 30" idea going horribly wrong
First off, most new players didn't really get the game upon reaching level 30 to begin with (hence the massive playerbase that still feed in bronze). Now you just shortened the learning for them. Second, you are going to have so many people in ranked matches without runes. "Oh, reached level 30, better buy my 3 more champs so I have enough to play ranked"...and they will Q up for ranked before having a full rune page. Then they will feed since they are really about level 20 without runes.
Literally the ONLY positive this has is for smurfs...and I don't think the game should be balanced around smurfs. Or players that have had their main account banned, and I'm not sure you should be catering to them either. Lower elo is already fucked enough, and you are making it worse. Hmmm...I wonder why you have a growing toxicity problem, despite your questionable at best attempts to fix it.