I think the root problem isn’t that M+ is bad, or that it is or isn’t content (it is).
I also don’t think the root problem is that there isn’t content to do or that raid, m+, etc is 90% of the content.
The problem is the content and storytelling is bad. If you took all the quests, areas, npcs, etc from WoW and submersed the player into a story and those NPC, learning about them, giving them a background, etc it would all feel so much better.
You also have all these towns and areas where it’s NPCs placed around standing, and the world doesn’t look or feel alive. If you look at Red Dead Redemption 2, you feel like the world you’re in is alive. NPC’s have jobs, lives, personalities, etc - they even change the world some over time. It’s not like they would even need a bunch of unique NPCs at every “town” in the zones, just do a few and make them really interesting and important to the player. Let the rest be filler, that are off doing things like preparing for war against the Jailer.
Shadowlands has given players a campaign, four covenant campaigns, a shards of domination campaign, and it’s easy to feel disconnected and well, nothing towards characters, even as prominent as the Primus. I think one of the major mistakes still was limiting players to one covenant, where players could have immersed themselves in all 4 campaigns and then selected a covenant talent that changed colors based on what covenant they aligned with, letting alts skip this of course, and then really helping a player feel something about each one. Side note - IMO they missed an immense opportunity for soulbinds and conduits to have been a skill tree like path of exile where players got to pick and choose amazing abilities/passives from different covenants.
It’s a great example of misguided focus on the destination (all these end game systems) rather than the journey. Maybe I’m off base, but if the journey to endgame was this amazing, unforgettable experience that made you feel something about the world your character was in I think people would feel much differently about the state of WoW.