Amumu passive

Amumu needs a new passive. Sure, flat MR penetration is nice, but most of the time you blow your entire combo before you can even land a single auto attack. This passive can only reach its full potential in the jungle, but Amumu's clears are so good that it renders the passive useless. Its just really outdated. Amumu needs a %ofhismaxhp scaling passive. All of the other tanks have them. Darius, Mundo, Gragas, Gnar, Illaoi, Malphite, Maokai, Nautilus, Sion, Poppy, Zac, Nunu, Olaf, Sejuani, Shen, Skarner, Tahm Kench, Taric, Vi, Volibear. The list goes on. Amumu is probably the only tank in LoL that doesn't have %hp scaling so it would be a really nice QoL buff. Thoughts?