I really enjoyed season 1 as well, but lost interest in season 2 after 3 or 4 episodes. I still intend to revisit again someday in case it just wasn't what I was in the mood for at the time. Something similar (but much shorter) is Hakata Tonkatsu Ramens. Like Durarara it has a large of cast of very eccentric characters who lives are all connected, but a word of warning it is VERY VIOLENT with dark humor (probably more like Baccano), so that might be a deal breaker.
I'm also watching the same currently airing series as you. As far as Demon Slayer goes, I think I'm committed through the end of the cour (episode 12 or 13), but not convinced yet whether I'm in for the long term, as most shonen series go on & on.
I couldn't get into Sun & Moon at all. Didn't seem to have any of the charm of the original series plus I don't like the new art style. I did enjoy XY though.