it's very debatable how far would community servers go, the community server browser is unuseable by default since there's a constant flood of fake servers + centralized slop, add that the remnants of this playerbase are mostly tradeshitters and/or redditors and you've got a rather explosive cocktail, tf2 classic (and this ignores other shitfests like pre-fortress 2 and open fortress) is inherently flawed on the basis of being completely different + being a tranny shitfest, that game is a fubar and it's best if it stays in its little nice bubble.
There's no more proper big subcommunities with their own decent gimmick anymore, it's all like you said; a bunch of subcommunities that all run 20-40 24/7 <map> servers, most of which are completely fucking dead and a waste of the hoster's money and resources.
Numerous big subcommunities which had created their own custom experiences have come and gone over the years. Two prime examples off the top of my head are:
SLAG Gaming had quite possibly the first ever custom weapon system in Advanced Weaponizer (and its sequel plugin AW2), and other fun gamemodes like Parkour Fortress and Wario Ware. Then they died when Jonas (Mecha) started focusing on A Hat In Time.
Creators.TF came along with a decent private economy system and unofficial content updates similar to what Valve would do, Admittedly, other communities (SLAG and RedSun as two examples) already had private economy systems and custom weapons, but there seemed to be more effort put into it by Creators than the others. Then they burned out in a blaze of mediocrity and interpersonal team-centric drama that was also fuelled by the general public.
It'd be nice if all these hosters running in excess of 10 servers would just shut down their extraneous servers for the better of the browser. It'd be nice to see another big subcommunitiy pop up with its own gimmick and revolutionize the game again. Sadly it's just more and more of the same old shit now. 24/7 this, 24/7 that. And shitty idle servers. I mean if idle servers are your thing, more power to you. They aren't my thing. And the trannies. My god, the trannies. God forbid you get on the wrong side of one of them and banned from one server, as you'll likely end up banned from a litany of other servers who are friendly with the tranny as a result.
I don't see TF2 going out in a blaze of glory. I see it going out with a choked whimper, surrounded by a cloud of interpersonal tranny drama.