If Riot wanted balance the game they should swap lane quests to class quests and use lanes as a malus/bonus
Since they want to keep that mechanic it would be pretty easy to balance the game with classes rather than positions.
Marskman might get the full item + 10% ad (number pulled out of my ass at the moment) but the latter is granted only on the botlane.
You can nerf cringe chapter and add the mana reg bonus to mages granted only on mid
Supports get their bonuses based on the supp item they choose
Top based if they are Juggernaut, tanks or fighters
It could open a whole world to the gameplay and we can stop heavily nerfing champs for their intended role because they go to another lane (Vayne)
You can even add a class a malus going to a lane since they don't want a class going to a specific lane.(particularly ADCs going mid and top)
Subclasses can help for niche style-gameplay picks and you are available to pick one. (Always using Vayne as example could either choose Marksman or Assassin style)
Game easier to balance, removing cringe picks, I don't see any downside of this idea in a season we're mages play 5 different lanes.