Not reading the whole discussion, but for my two cents....
Yeah, the mob villains still serve a function. Bendis used them in the not-to-distant past. And isn't the CW show using Intergang right now? The new Superman cartoon did a riff on Intergang too, and I think the subplot of who's pulling those strings is still hanging? If you wanna look back a little further, we also saw mobsters in the 90's cartoon. I feel like they're around. Maybe at the edges but they're around.
Modern writers don't seem to use the mob very often it's true, but they're somewhat out of fashion aren't they? I don't see a lot of mobsters in any of my fiction these days. At least not in prominent roles. Daredevil is off fighting demon ninja cults or something (I need to catch up there) and Batman is fighting his own super robots across the multiverse or some such weirdness. Arrow's jumping timelines and screwing around with Waller. Bludhaven had Blockbuster, but he died at what, the end of the first year? Granted, my pull list skews towards the high concept stuff like Thor, Supes, GL, etc., so maybe I'm missing some good mob stories?
Feels to me like we're more likely to see corrupt businessmen or politicians, or radicalized /domestic/ terrorists these days, at least as far as 'real-world villain proxies' go. Maybe the idea of the mob just seems a little too....quaint?.....to be a big scary villain right now, when government itself is being eaten by conmen, and mobsters look honorable and reasonable compared to the lunatics shooting up schools.
But I feel like Intergang, at least, still has a minor but fairly consistent presence in the Superverse. And I think I saw some scans of a Williamson issue with Red Cloud? I dunno if that was just a 'random bad guy' thing or if it might be hinting at more but I feel like the invisible mafia would fit Williamson's run real smoothly.