Shift back some power from Darius' Q to his ult
You want him to be a dunking machine?
Then reduce his Q base damage and increase his ultimate damage instead.
Like this:
Decimate:
Blade Damage: 40/70/100/130/160 >>> 20/45/70/95/120
Noxian Guillotine:
True Damage: 100/200/300 >>> 150/250/350
More powerful as a dunking machine, but his laning is less oppressive and you can actually fight him.
Thoughts?