Isn't the fact that tanks outdamage assasins (IE FULL MTANK Akali) a bit bs?

Assassins will always do more damage than tanks. The reason why it feels like tanks do so much damage is because you're not building any resistances. Anyone can kill a squishy, but that's not to be said of tanks. Because tanks live longer, they are able to push out more damage, unlike squishies who die.

You don't see tanks catching people out and killing them (unless it's Nasus or whatever)