How different would this game's balance be if everything did 50% damage?

This isn't a suggestion! I'm just thinking about what it would be like. Regen would be a stronger combat stat on pure tanks since it would have more time to be applied during combat, Burst Mages could play riskier but couldn't burst as hard, Assassins would be a joke, Tanks would reign supreme, ADCs would be even more important for their sustained damage capability.

RIP Poke Mages in such a meta. Mana costs would have to be slashed in half thanks to the increased damage needed to kill a champ.