An idea to make Tanks tank again: Give them an item that can help protect against Penetration?

Before the penetration rework when Flat Amount was Calculated before % Penetration, tanky builds work (unless you're up against Vayne of course). But soon after it was changed, armour/MR became so unsatisfying and obsolete as a result. Everyone wants to be glass cannon and bursty. If we reverted that change though, a lot of AD Casters will become obsolete again, as you all remember, Zed was pretty shit upon release.

So how about this then? Keep Penetration the way it is. BUT, introduce a set of items or perhaps a new stat or mechanic that is designed to mitigate the effects of penetration. Like reduce the effectiveness of any % penetration the enemy hitting you will have. All Tanks need is some form of protection against penetration and they can start feeling strong again.

Because at this point right now, the only tank that actually feels like a tank is Maokai, and that's because his Ultimate helps counter-act % penetration by reducing damage taken by % as well.