untargetable vs. invulnerable

So with the current set up, certain champs have ways to go untargetable and not take damage , these are the ones that can do it for longer than a split second . There is also the item all of these things make it so that champions wont take damage, and sometimes are rooted in place. I think that the champion abliities should be changed to untargetable, but not invurnable. This means that the champs could still take aoe damage, and be affected by spells with no target such as a karth or varus ult. I would suggest that zhonyas is left the same, as the only means of invulnerable item. An arguement could be made for liss' ablilty as it is an ultimate. This would make it less anoying to play against the champions leaving more counterplay in champion select and in game. The trade off would be that the champions affected would get actual compensation buffs :( For example vlad's pool could go from 20 percent current health to 10 or 5 percent. Fizz could get some of his damage back. Liss would be harder as her ability is an ult and she is already fairly good. That is why I think I would leave her alone.