Nasus was supposed to be the model

For juggernauts, they claimed that Nasus was the ideal they were modeling the class after. He has lane sustain, but needs to ramp up his Q over time to become a force to be reckoned with. He has no true damage, coupled with a heavy tendency to build solely tank items. And his heal is lifesteal, meaning it's based on the damage he actually deals.

So of course, not a single one of the juggernauts reworked or created at the time had either of those drawbacks, and only not only matched his strengths but have amplified versions of them.

Darius has high kill potential from level 1 against most top lane opponents. His heal is a high amount based on whether or not you hit the opponent, regardless of how much damage it dealt. And unlike Nasus, his extra 1000 damage late game is both free from leveling up and True damage.

Illaoi also does not have to build damage for her damage or heal, and likewise does not have to work the way Nasus does to have it. She may not have true damage, but unlike Nasus she is a threat to the entire team in a wide area-- not just one person sometimes.

Mordekaiser was forced into a class he wasn't a part of with so little thought put into his numbers that a pro player picked him with no practice and carried the match. Before that, Mord players were building him as a burst mage so that he could quickly get a ghost of the enemy's ADC or mage to increase his own damage.

Garen, like always, is still just a weaker version of Darius. But was given hefty true damage on a specific target and increased healing outside of combat.

But what these champions all share is a relatively strong early game that, in the right hands, scales into a near unstoppable mid and a nonexistent late. Which is not at all like Nasus, who has a weaker early, needs to keep stacking mid, and then becomes unstoppable late after his team has paid the price for his farming needs.

Juggernaut shouldn't just be a tank class that emulates the high damage and durability of a true to life tank more than the latter. They should require time to scale up, with strength in patience. What they should not be is an unstoppable force that you have to pick around or lose to with no in between.