They reworked him to tone-down his historically low-counterplay laning phase, in exchange for giving him much better late game power.
Well, he's a bit weaker early on but he still can dominate most melees. Only difference is that he actually has a way of dealing with ranged matchups now thanks to his heal, essentially removing one of his main weaknesses. His late game is a little stronger now but it still is terrible against a team with any sort of peel.
One of the rework's goals was to change his playstyle from "If Darius didn't obliterate his lane opponent then he failed" by giving him other ways to be useful to his team and helping encourage him to teamfight by giving him bonuses for hitting multiple targets and reducing the windows for him to get peeled, because previously his teamfight was so bad that he would just default to splitpushing most of the game. Yet in the patch overview video (5.18 part 2), when talking about the Darius balance changes, they explicitly stated that they were tuning him so that he would be good at shutting down his lane opponent and punish him for letting the game get to late, saying that he didn't do his job right if the game got to that point.
SMFH
Regardless, if you're melee you should actually try to stay right next to him during his Q. It denies him the heal and you take much less damage, and now that he doesn't have insane base stats anymore you should be able to win a melee trade against him if you dodged the axe blade.