Darius Balance Suggestion
R - Noxian Guillotine Now Consumes all stacks of Hemorrhage on it's target.
Why? Darius is getting automatic kills on low health targets because Hemorrhage will cause them to bleed out even if the Darius doesn't have enough skill to properly time his ultimate. Even if he used R to soon and lets the target walk away alive his passive secures the kill.
What a player will have to do? Make a skill based choice. Does Darius need the hemorrhage stacks or should he attempt to cash them in for a killing blow?
Does it follow your theme of that champions have moments of strength and weakness used on other champions like Ryze and Gnar? Yes, Darius now grows in strength, but instead remaining deadly for huge amounts of time at the end long fights he must decide when to cash in his extra power and attempt to finish kills with R.