Can tanky damage items not do flat damage?

I mean, flat damage always screws the adcs over more than anyone else. Not really fair if you ask me. If you made some slight changes to tank items to make them more for tank-vs-tank situations, that'd be good. %Missing health damage Returns %of the damage blocked Slow and reduce armour instead of massive AOE damage Small %Max health damage that increases with each consecutive auto in combat

I know those are shit ideas, but come on. Anything other than flat damage.