Darius May Be Balanced...
But he isn't exactly fun to play against. He has an amazing early game, decent mid game, and a somewhat worse late game. Out of all the Juggernauts, he was and is the most successful, but he just isn't fun to face. Play a melee laner, and you're basically screwed. Play a ranged laner, poke him down, hopefully dominate him and you can still lose to him mid game. I know there are a few counters to Darius, but I (and I'm sure others) don't find it fun to learn a counterpick for just one champion because literally 90% of the rest of the champion pool can't do crap against him. I'm not saying he's overpowered, but he does seem overclocked to me. Compare him to the rest of the Juggernauts:
resembles Darius with his ult. While Darius has to stack his passive bleed to get the most out of his ult, Garen has to wait until his opponent is somewhat low, or his villain, to do anything with his ult. Additionally, Darius' ult unlocks at rank three, so as long as you get a kill with your ult (at rank 3), it automatically cools down. Garen has an opposite power curve than Darius: weak early game, passable mid game, and powerful late game.
The original Juggernaut's Juggernaut, Nasus has to take extra care farming and, unlike Darius, reaches his full potential late game. Also unlike Darius, Nasus has a nasty habit of losing early trades hard. In the current meta, he feels weak to me.
Objectively a failure. Skarner is a jungle Juggernaut that I find tons of fun to play, but just not that impactful. The spire minigame is interesting, but the counterplay is to literally stand on them. I feel as if the passive was swapped somehow with his W, Skarner would feel better.
I see him complained about on the boards all the time. Not because he's overpowered, but because he's riddled with bugs, weaknesses, and has one of the slowest base movements in the game.
Of course, maybe my opinion doesn't matter cuz I'm a bronze casual, but that's just how I feel. TL;DR, It seems to me that, while Darius is balanced, he's not fun to play against at all, and the rest of the Juggernauts underperform in every way compared the poster-child Darius.
are all horrible, archaic designs who im sure riot would dumpster if they ever became prominent in the meta
are leagues ahead of their peers in terms of design