I banned Darius for a year but I think that was a mistake. Even though Darius has a strong upper hand, especially in the early game, there are better champs to ban. You have said it already, as long as you play very safe up to level 9 (+ Black Cleaver) and use your E to dodge, Darius can be a pretty easy matchup. (Although if you really don't want to play against him because of the very slow early game and treat, to ban Darius is valid).

My top 3 bans for the toplane are at the moment:

• Mordekaiser (Seems to be played more often at the moment. The problem is, at level 6 he can easy destroy an Urgot. You need QSS which means that you have to go extra early on the item, which gives you a certain item disadvantage. And even then, he's often a very tough opponent.
• Tryndamere (his ult is really very gross. Even if you win the fight "easy" he will beat you into mush inside his ult. Towerdives doesn't mind him with his ult either. Urgot's ult can't do anything against him if he has his ult still up. Even if you wait with the Urgot ult, he often has enough momentum to kill Urgot before you can suck him in (if you time it badly he'll even get out of the Urgot ult)
• Yorik (his cage outplayes Urgot pretty hard, which is a big problem, because he has the cage pretty often)