He's meant to be oppressive and a powerful duelist, and in some matchups hes good at this job....primarily those who have noticeably weak earlygames (such as nasus, any tank). However, with so much burst/poke in the meta, Darius (believe it or not), struggles against this poke/burst. A few seasons ago, Darius used to debuff enemies hit with his empowered auto (his W) with a 50% AS debuff, but was removed as it made him too oppressive. Now, with all the monsters of rivens, jax, etc, Darius really struggles to duel anyone who doesn't have a weak early game.
take a look at this old video (https://www.youtube.com/watch?v=XyIZ0q9DvkY) , in which the developers of LoL describe all champions (by November 2018) briefly. At 9:15, they talk about Darius. They describe him as a badass person, who if you see in lane, kind of have to think "oh i probably won't win lane". That really isn't there with all the other monsters toplane. So please, either nerf the damage toplane (but we all know that won't happen), or give my boi darius ( and some other juggernauts/tanks), some love :c
EDIT: forgot to add in video link oof