Take a moment to realize Nasus needs some help.

He needs some help after the Armor nerfs. His gold income is from farm until he is confident and strong enough through stacks and tank items to fight is enemies and get a kill or two. So armor being more expensive and less effective for a person like Nasus is tough.

And if you want to compare him to the other Juggernauts and characteristics that they have he is lacking. So Juggernauts are supposed to be pretty tanky and hard to kill.

Compare that with Darius who has a much better heal which gets pretty insane if he hits 2 to 3 targets. And his bare armor and armor at 18 is way better than Nasus. Nasus also needs many stacks for his Q to sustain him decently due to his passive. And if he is in the front line and has to fight another tank with Armor his Q wont deal much damage thus giving him weak sustain and barely any at all when his Q is off cooldown.

Compared to Garen his Armor is about the same but Garen ends up with more because of his W stacking up to 30 armor and MR. He doesn't have sustain in battle but he also can use his W for 30% damage reduction. So Garen is tankier than Nasus from not only stats but with Damage reduction.

And compared to Skarner his base and armor at 18 is amazing compared to how weak Nasus's is. And Skarner has a % max HP shield that lasts up to 6 seconds long. The only way Nasus can get tankier is from using his ult. Its decent but it is an ultimate, every other juggernaut has some way of reducing damage that isn't an ultimate and is arguably stronger than Nasus's because he gets kited and shredded anyways.

So with all of this and comparing to the other Juggernauts. Nasus is very lack luster when the name of the game is snowball and get fed early. And even then so Nasus has the weakest late game of them all due to him being kited massively and having the least tank stats and steroids. Even with stacks it takes time and is very selfish. He already has enough problems. The armor nerfs hurt him a lot from how much gold he needs to be a tank. While also being stack reliant and wanting to at least have the luxury of having a Trinity force.