Don't buff Darius dmg
Riot i agree darius needs buffs, i already expressed my feeling here on that, but after playing him a lot more i think buffing the dmg will make him overbearing in lane, even worse buffing the heal, the heal is actually obscene if used well, i killed ppl with 10% hp while they where full hp after getting the passive on someone else, i just run away from the full hp enemy and spammed Q and W, i was uber tanky so he didn't have enough dmg to kill how much i was healing every 3 secs and ended up dying from bleed Q spam and W spam. He is already good in lane if build/played well, the only charc that raped me more than once until now was fiora, and that's only because she is OP af right now.
What he really needs is help after lane, if you buff the AS like you said you would he will be fine in terms of dmg with the AS alone, what he really needs is a buff on the E in terms of range, it's a joke right now ppl actually troll darius almost in is face knowing how little the E does, i would prefer you buffed the range and removed the slow on the pull which is kinda obnoxious to play against and with more AS he doesn't need it, another thing you could do is put the old MS buff on the Q when it's used on a bleeding target, he really needs help out of lane like he used too the bugfix on E made it even worse out of lane to do anything if you are the only tank and ppl want you to engage, it gets into a joke fast even if fed af from lane, you know like old darius...
TL;DR- Don't buff the dmg, buff the AS only and the engage and stickiness and he will be fine. Or the rework fixed nothing and just made him a slower version of himself with the possibility of being more dangerous in TFs.