prepare for TBC classic
retail is in no way dead. but to me it seems the target audience of retail is far far away from the classical „wow raiders“. what i wanna say: the game (retail) seems to me like its goal is to attract more casual gamers, by Covenants and „systems“ and to attract hobby pseudo guilds, a form of a heavy loose coupled grp/ppls, doing a bit stuff together, not much more coupled than a PUG grp, meeting once a week for a few activities here and there. in my exp the „real“ guild and the „real“ raider community got very very rare. wether i say there arent any, nor i mean this in some „hardcore player“ sense. to me it just seems like „modern wow“ distracted many players of a specific type (and exactly this type is interessted in mythic raiding) while it attracted another type of gamers. you may call the distracted ppl „oldschool“ if you wish.
so, maybe, a crowd that is more interessted in stuff like mythic raiding or strong guild communities or social aspects in a MMORPG etc. is maybe easier to find on something like TBC classic, than in „modern“ wow.
but maybe thats just me and my experience. i wasnt on wowprogress etc. to have a look at the number of mythic raiders and if it decreased heavily in comparrison to lets say WoD or so. its just how retail feels to me nowadays. but maybe thats just me.