Did you read even what you quoted? "But he's nowhere near op, so if he got this change then he would need to get the rest of his kit buffed accordingly." That's what I said.
He could use a hugely increased scaling on his Q. His Q starts to get really weak once the game reaches a certain point. An increasing mana cost on his ult shouldn't be much of a problem. It would just stop him from being tempted to spam his ult for every single kill, which is a big reason why people don't like having him on their team. What happens really often is it's not even necessary in the slightest for Darius to ult but he uses it anyway. If he had some damage put into his other abilities, he could still contribute the same to teamfights without having to "secure" kills on people that would've died anyway.

Thank you for pointing out my mistake. I quoted the wrong person. Not going to edit the original post. As for the increasing mana cost on his ultimate due to players spamming it, it is ALWAYS the players choice whether to spam his ulti or not, to deny their own team gold or not. What about the ones who could Ulti 'spam' but choose to let the carries get the kill? What happens if you are forced to use your ulti because your team doesn't want to secure the kill or leaves it to you? What if you get into a situation of cleaning up a team fight but you can't bunnyhop to clean it up because everytime you do it's mana cost has increased?

Other bruisers are quite capable of going on 'KS' sprees, it's just it isn't as commonly reported as the Darius ones. His nature of relying on hemorrage stacks for the double ulti damage means that noxian bunnyhops are hard to pull off, considering his ulti's lackluster damage when you build him bruiser.

With Darius being a pariah and generally hated by the community, along with most people and their innate instincts to follow the masses (whether they choose to or not, 90% of people have followed a majority number in some way, irrespective of whether the idea is logical or not), most cases of Nerf Darius ulti, or remove Darius, can be attributed to a collective desire to be rid of him, but I imagine most of them haven't played as Darius long enough to see his glaring issues in relation to the other viable bruiser picks.

I will say though, you are the first person in quite a while to agree with a proposed change (usually a nerf) and actually say that you have to buff somewhere else in his kit to make it fair.

Cause it's not like you have to go near him to CS ever or anything or get zoned...

I'd go through and list all the champions who can CS just fine, fight evenly with him, and even beat him into the ground, but you're probably too dead set on the "MUST RIGHT CLICK DARIUS TO WIN" mentality.

Beating Darius is 50% kit and 50% execution, roughly. Get better.

HAHAHAHHAHAHAH you serious?

You forgot that Garen's ult is easier to use on high health targets (tank execution).

100 seconds is plenty of time to steamroll an ultless darius's lane... What do you mean he doesn't get punished?

Or did your team not go capitalize on his ult being down after you made sure to tell them... you did right?

For those who still think he's OP

http://na.leagueoflegends.com/board/....php?t=2391118