I feel like it involves lots of dark themes, but they didn't carry much weight with me. As you said OP it involves drugs, sex, hyper violence etc but it all felt predictable enough, and that not enough contrast occurred that it really upset me. Other than the stuff with the little brother, the darker parts didn't really resonate with me. I think I'd enjoy the manga more as it's supposed to take its time, but not much of the anime really shocked me, even the little bro stuff.
Not enough down time, no contrast between the dark themes and light ones.
I'd say that 'A Trail of Blood' handles dark better, but in a different way. More disturbing and psychological than shock focused, which I feel devilman is more of the latter.
Probably just my tastes in the end though.