They're buffing Darius? Why?

This is not to QQ about him being OP (though my teams frequently lose/struggle against an enemy team with a Darius at late game, so if you think he's OP I empathetically understand why), but did he really need to be buffed? The reason I say it's not a QQ is because when it comes to completely resetting his R at rank 3, by that time the cooldown is so low that without (much?) CDR if he dies or misses the window, its up before he's ready to use it again.

But I can't tell you how many times I've killed or gotten away from a Darius, that has more or less destroyed our team, because he was out of mana to continue chaining his ult for a quadra or a penta, and now that small advantage is gone. The reason they cite is to make up for his general lack of mobility and saying he falls off late game. I am not claiming to be well-versed in the mechanics and strategy of this game in the least bit (and if I was, I'd especially not claim to be on this boards account because I can't get it out of bronze, and people here like to judge your opinion based on your rank), but does he really fall off? I want you guys to tell me your opinion, but I feel I'm mostly going to get the typical " is garbage. You're just bad." because it's the typical response I see, regardless of the champion, when someone expresses having trouble or claims of them being overpowered. If that's all you're going to say then it's not helpful, I want to understand why he's garbage, because his lack of mobility hasn't seemed to hinder him for me. Perhaps every single time we've ever gone against a team with Darius, the skill difference between teams is so far apart somehow, that it just ends in us playing really, really badly, and if we got better, Darius would be garbage. But otherwise, the only time a Darius fails to be the unstoppable force of damage that's burned in my memory is if both he is shut down early and the game ends before 25min (maybe 30min)

But again, my intention isn't whining, it's me expressing confusion based on my experiences, accepting I am terrible at the game, and asking a better player to make it more clear how badly Darius needs this.

(link and the information provided in that link about Darius): http://www.surrenderat20.net/2015/03/red-post-collection-champion-mastery.html#10 3/11 PBE update's changes to Darius' R (significantly lower mana cost and if rank 3 R kills target it's cooldown resets entirely), Meddler explained: "Yeah, late game power's the goal here. We originally removed Darius' full ult reset because it lead to situations where he'd kill you once with it in lane, get ahead and then always be able to do so again, leaving opponents with no way to continue laning. Late game by contrast we don't think a full reset will be problematic, particularly given in many cases the reset window gives you all the casts you can use anyway. Late game's also where Darius particularly struggles to close against many team comps, so giving him the potential for a bit more payoff if he can there seems appropriate. He's gated heavily by mobility, so doesn't need to be as mana/CD gated at that point (the Nasus principle)."

((Digression: How come practically every new champion lately seems to have insane mobility? Maybe I'm just being paranoid, but it makes me start to believe the posts I initially dismissed about Riot only caring about LCS and the ability for championship teams to make high-mobile plays for entertainment value.))