Lets face it, the only way to balance this game would be to rework every champion from scratch...

We are way too deep into the powercreep to do anything right now.

Anyone who is not a tank or ADC feels like they barely matter, and that wont change anytime soon. Tanks deal way too much damage, ADCs are like ranged Assassins that nuke per second rather than damage per second, and everyone else just suffers from that.

We would need to have each class totaly reworked to fit the role they are supposed to play.

Tanks have to get stronger/more reliable CC but way way way less damage than they deal right now, especially the % max HP dmg has to go away, Assassins should be able to actually Assassinate someone again, mages should be back to high nuke on CD glasscannons, and ADCs should go back to deal ok damage with each attack, but on a constant basis.

I think the best ADC to look up to for a perfect balanced concept is Ashe. No insane crit burst, no inbuild escape or survival power, and her only hard CC is her Ultimate.

ADCs are an important part of the team, but right now, if we place Mages and Assassins on a 5 on a scale from 1 to 10, ADCs would crit the score for 25, and thats just not the way it should be. Same for the Tanks. To play a Bruiser feels like a waste of potential, because lategame, a real tank will deal nearly as much dmg as you do, because they all got %HP scaling dmg, but they are of way more use to the team. A Tank shouldnt just run into the enemys backline and beat the mage to death while barely getting scratched himself.

But well, I think this is never ever going to happen. RIOT would have to set everything aside for like at least 2 month or so and just get everyone on work to rebalance every singel Champion in the game from 0, and well... we all know you would sooner see Trump building a Gate in the texas border fence with a Sign that says "Welcome Mexicans".

EDIT. Forgot this: Items have to change as well.