I think m+ is definitely the main source of retention right now. It’s just 5 people, only requires short time, gives the strongest items in the game, probably much easier than mystic raid, doesn’t require much development time. Clear winner.
Unfortunately I quite hate it. I dislike that it’s timed, that it puts so much pressure on routes and healer dps, and how that trickles down into class design, how it invalidates raid gear.
As somebody else said above - the M+ culture certainly isn’t doing WoW any favors. It turned it into a zoomer game. Rush rush rush, quick quick quick, ugh.