Darius is an "all or nothing" champion. Where if you happen to be another melee you'll be going home with nothing. Olaf for example cannot win top lane by maxing E, he can trade great, but you'll shove the lane into his tower and without Q maxed his wave shit is clear, so provided you don't keep commiting suicide you'll outscale him and reach his weaker late game. But what do you do vs Darius in this situation? Like when Jax can't beat him, and Jax is possibly the only melee hypercarry the game has seen (Tryndamere is a maybe) as well as possibly the strongest 1v1 in melee situations, doesn't that tell you something is wrong?
Also on Ghost/Flash, Wingsofdeath plays Darius with both, he don't need no ignite, just stay on people and they're gaurenteed to die before you do. Darius ult doesnt even have that long of a CD 100/90/80 compared to Garens 160/120/80 (this ones a joke btw, 160? fix that shit Riot.)
On the topic of broken vs balanced. Lets grab Vayne. Vayne has what Riot have confessed to be the most broken ability they have ever put in the game, Silver Bolts. They have admitted that there is no way in hell to balance this ability and they regret ever putting it in. However is Vayne OP? No.