Hi everybody, CertainlyT here.
First off, I don't think anyone's elo is relevant to this discussion, for a few reasons:
First, we have a populist design mentality -- LoL isn't for the top 1%, it's for everyone to have a great time playing;
Second, one's elo is not a perfect measure of one's understanding of the game. We observe that a lot of top players succeed due to amazing mechanics.
As to Darius being a toxic influence because he deprives his teammates of kills, I think that point has some merit. We discussed it internally several times during Darius's development cycle. We concluded that the benefits of an ultimate like his (in terms of sheer epicness and diversity amongst ultimates) was worth the cost, even if it did "steal the spotlight" from teammates on occasion. It is not something we intend to put on many future champions, perhaps none ever again. We justified our decision to give Darius his ult on a few factors:
1. Our community is continually maturing. Players have the savvy to look beyond KDA to assess their contribution to their team's success. They feel good when they heal their teammates, make defensive plays, coordinate their CC, etc. We think Darius players will know that it wasn't solely their own efforts that got them that double kill and Darius teammates will know that it wasn't just Darius doing damage in a team fight.
2. Once Darius has a few months under his belt and his popularity inevitably wanes a bit, this will be less of an issue since you'll have fewer teammates as Darius on a per game basis. Most posts from those frustrated by Darius are those who seem to be seeing him game after game after game. It's important to think about game health not in terms of momentary snapshots, but long term.
3. Darius's eventual role in team fight scenarios is fundamentally altruistic, probably in the mid-field using Apprehend+Crippling Strike to peel diving bruisers for his ranged AD/mages and follow up on those champs' DPS with an armor ignoring finisher. He doesn't have the defensive steroids or the mobility to leap straight onto enemy carries in the same way Irelia, Jarvan, or Jax can. Even as a tanky man, he is a dps soak -- enemies are encouraged to burn him down to stop his kill chain, shifting focus from squishy targets.
4. Darius is a great candidate for aura items. He benefits dramatically from Reverie for the burst of MS so he can position himself for that speed boosting Q, Randuin's for the slow to let him manage his Crippling Strike a bit better, and Aegis of the Legion for the balanced defensive stats it gives. That gold he "KS'd" can and should be put to good use. I don't think you will see many Bloodthirster wielding Darius's in 1-2 months. I know I feel at ease when the guy that grabbed the kills in an early teamfight puts that gold toward an item designed to help us win the second (Internally, the running joke about me is that I insist the first team to buy an Aegis wins).
5. Darius doesn't just kill steal -- his ult is a lot of the power on his kit and contributes to sealing a great many kills where the enemy might otherwise have escaped or continued dealing damage for some time. I think from all the "Darius OP" threads we can agree that he certainly holds his own on the battlefield at the moment. If his ult was some sort of Blitzcrank passive that automatically zapped any champion below 200 health, then you'd have a stronger point.
I hope that clarifies our reasoning for Darius's ult a bit. This game is a complicated and wonderful beast. If every champion's kit was hardwired to have their kill total reflect their total contribution to kills, it would require pruning a lot of abilities from the game (all % missing health effects, mundo's cleaver too!, etc.). The resultant lack of diversity would be a loss to our players as a whole.
Secondly, I completely agree with everything you said and I think this post needs to be stickied to the from page. The flood of straight up Darius QQ on the forums is insane and completely unwarranted.