Tank Busting Champs

I know there are Tank busting champs (Vayne's % Max Health True Damage) but these Tank buster's also do massive damage to squishies.

Just for argument's sake what if there was a tank busting champ that (taking it to the absolute extreme) did all % Max Health True Damage (no flat damage, no physical damage, no magic damage). Interestingly he would kill a squishy with 40 armor and 1600 health at the same speed as a tank with 4000 life and 200 armor.

This is just an extreme example to prove a point and obviously the champion wouldn't be designed to have 100% of his attacks do % Max Health True... but if a significant portion of his damage was implemented in this way he would be in a unique spot. His damage against squishies would be significantly sub-par (not like Vayne who does crazy damage against everybody), but damage against tanks would be significantly above average. Just an idea.

Even if in this 4 tank meta you don't see tank buster's like Vayne so something seems off with current tankbuster's design.