You do realize that Darius is no longer slow? Runes are overabundant at making him move fast enough to keep up with bursts.
He also has taken to getting

44% are also taking 
And when a Darius whose good is close to Karma, he doesn't run in a straight line...... he waits for Karma to Q....... and Flashes past it. Which puts him in range to Apprehend. Which = dead.
Karma CAN build an insanely fast rune page and items to try to combat this.... but the tradeoff is..... when he Ghosts..... she has less defensive stats, less AP, and dies more absolutely.
Yet.... if you build tanky, you're now subject to being perma caught, and having your armor shredded.
P.S. Who brought up Karma top lane vs Darius? I just said Karma vs Darius... I didn't say where Karma was playing. This is a team game.
Also, to get close enough to really W Darius, you DO put yourself in Apprehend's range. Try the lane sometime. The second you W Darius, you will get pulled.
I still don't know why people EVER would build Sunfire on almost ANY champ. Much less a Karma? Sunfire's entire expression is: I have no CDR, can't last hit mobs, and wanted a tiny bit of non skill damage. Cinderhulk works because of the Bonus HP mod, and because some junglers are melee face tankers. There are so much better picks top lane than a Sunfire..... Most Sunfire builders end up feeding.