You get practically nothing back unless you land your Q on 4-5 people. Unless you're playing in Bronze the enemy team probably wont let that happen. Its only use now is healing a smidge on your lane opponent to try and save potions. Hell, you'd probably be better off just starting corruption potion anyway. Maybe just remove the heal and buff his defense or HP/HP regen?
As a darius main with all the darius skins (yes, even the $400 dreadnova) and mastery 7, I can safely say you know nothing, jon snow yung padawan.
The heal is quite relevant in lane, it makes it almost impossible to meaningfully trade with him because he will heal it back soon enough. Not to mention that sustain used to be his only exploitable weakness as a pure melee laner against him. Now even that's off the table.
The heal comes in handy more times than can be counted, even if it is a small amount it is still that much more life you have for a few more moments. And, if you build Spirit Visage (always should unless enemy team is all AD) than that heal on his Q is even better.
I can see his HP rise in an annoyingly large chunk every time he hits it laning. Your argument is invalid.
