Notice out of all the Juggernauts how Mordekaisers the weakest?
I mean literally every other juggernaut is at least SOMEWHAT viable,

are all at least decent juggernauts while
just seems....well.....
I mean primarily because most tank items are AD + Armor and/HP while very few are AP + Armor
being the only 2,
a large percentage of AP tank items are either AP + MR or AP + HP
now yes Mordekaiser uses HP to use abilities but the problem is is that HP on it's own isn't enough, as he doesn't have the damage to use without sacrificing HP, if anything should be done to make Mordekaiser viable again, he really should get armor/MR scaling due to the lack of much defense while trying to build damage.
to list a few that are defensive and AD supportive, which as we all know, every other Juggernaut's AD.
to list a few items that are both defensive and AP supportive.