The Evolutionary Dead End of "Rune's Reforged"

Riot have come across an evolutionary dead end in game design. They cannot have ruins that increase mobility (since Assassins and Bruisers) have so much power that they would take these and break the game. They cannot give too much utility because that again makes Assassins and Bruisers too powerful since most are supposed to have little CC to make up for their huge damage. They cannot give proper defensive options because Tanks would become unkillable again and the LCS would suffer as organised team love those sorts of things.

So what can Riot do? They can essentially offer nothing but damage which causes its own sets of problems.

The problem is that EVERY tree is available to all champions. So they solution is to limit rune choice to different champion classes. So that there are no unexpected interactions or design that Riot never intended.

If Riot don't do this, the new rune tree is just a dead end they can do nothing with.