I think i understand why ppl complain about darius quite often, specially in lower elos
Because its a lot harder for you to beat darius than it is for him to beat you, assuming you're playing a melee lane.
Say you're playing someone like riven, for you to cleanly beat darius you have to play the lane perfectly and not fuck up a single trade, extend 1 trade too much and you have to pay with flash, extend 2 and you die and lose lane, and even when darius is 0-3 he can rush ninja tabi and still destroy you with ult if you fuck up a single trade if he ever gets to 5 stacks.
Add junglers to the equation and you can see why he creates quite of unfun experiences, even more for players who arent prepared to deal with it, and honestly even in diamond i feel like i have to work so much harder to beat a darius compared to what he has to do to win a lane (basically just get into his 5 stack minigame to win regardless of how poorly hes doing).
can still penta in 0/x