Create a champion with a choice

It seems that Riot is all for a champion being able to build both tank and assassin and be more effective with the tank build.

If that's the case, why not just create a champion who's given the choice at the start of the game whether to be a tank or assassin?

It could be that in shop, you purchase one of two items: a Shield or a Sword. The Shield changes all of your abilities into low damage, high-cc abilities. The Sword changes them all into high damage-no CC and/or mobility abilities. You cannot switch your choice after 5 minutes have passed.

With this, there'd be a champion who intentionally can go both roles, rather than just being a broken assassin design that they refuse to fix.