Why Mordekaiser's base stats are so low?

Compare them to Darius, another juggernaut (which is why I want to compare him to Mordekaiser)

• Health at level 1: 582
• Health at level 18: 2282
• Health growth (base health gained per level): 100
• Base health regeneration at level 1: 10
• Base health regeneration at level 18: 26
• Base AD: 56 - 141
• Armor at level 1: 30
• Armor at level 18: 98
• Movement speed: 340

• Health at level 1: 525
• Health at level 18: 1766
• Health growth (base health gained per level): 73
• Base health regeneration at level 1: 4
• Base health regeneration at level 18: 9
• Base AD: 61 - 146
• Armor at level 1: 20
• Armor at level 18: 84
• Movement speed: 325

Fun facts:

1. Darius has the third highest base health at level 18: He only loses to Tryndamere and Alistar.
2. Mordekaiser has the seventh lowest base health at level 18: He wins only against Gnar (mini form), Anivia, Zilean, Zyra, Nami, and Heimerdinger.
3. The only champions that have a lower base health regeneration at level 1 than Mordekaiser are Soraka and Gnar (mini form)
4. Even before the buffs, Riven had higher health regen than Mordekaiser
5. Darius has the third highest base health regeneration at level 1. He only loses to Sion and Heimerdinger.
6. At level 18, Darius only has lower health regeneration than Heimer, while Mordekaiser has the lowest health regeneration of all champions at level 18, with even Soraka and Gnar surpassing him thanks to their growth per level.
7. Mordekaiser's base health regeneration at level 18 is lower than Darius' base health regeneration at level 1.
8. Mordekaiser actually has an higher base AD than Darius, at level 1 and level 18. It is the only base stat that he has that is better than Darius. That said, Darius still has the third highest base AD at level 18.
9. Mordekaiser's base armor at level 1 is between the 20 lowest base armor of all champions, while Darius has the second highest base armor at level 1.
10. Mordekaiser's base armor is actually decent at level 18, but Darius still has the third highest armor at level 18.
11. Taking into account only base stats, Sona is actually tankier than Mordekaiser, despite the fact that everyone (jokingly) says that Sona is squishier than a minion.

And then I ask. Why Mordekaiser's base stats are so low? Why Darius is allowed to have way better base stats than Mordekaiser, even though Darius has a much better early game, snowballs better, has better sustain, and has better 1x1 potential? Darius even has CC, while Mordekaiser has no CC at all (he is required to build Rylai).

Granted that Mordekaiser has his passive shield that technically adds to his health, but with Mordekaiser's base health being so low, the shield does not seem to be a bonus. It feels like a compensation for his base health being so low. It is the same situation as Sion: his base health is so low that in the end, the bonus health that he gains with his W feels more like a compensation than a bonus.

You may say that Mordekaiser usually ends up building or , which is why his base health regeneration is so low. Here is the thing, though, with Darius having a better sustain in a portion of his missing health being restored, he doesn't even have to build sustain items like lifesteal or spellvamp. He may build but in the end, this is not necessary, since his natural sustain usally is enough.

Also, while Mordekaiser is manaless. Darius' mana costs are low enough that being OOM is not a problem for him. While Morde has to spend health, therefore he essentially kills himself each time that he casts his spells.