As a staple of a major patch? Yes. Or at least the current game directors feel that way (and have expressed that repeatedly.)
Well, considering we don't know what Delves include or how elaborate they are (especially when they said they're non-instanced) probably. 10.1.5 was a huge patch. I don't see why they would have felt compelled to call 10.1.5, 10.2: We'd be having this same conversation if 10.1.5 was 10.2 & 10.2 was labeled 10.3
Unless there is a huge shift in the dicotomy, Raids are the endgoal of all content, both competetively and narratively: Dragonflight has had a lot of content, but its raids have been smaller than in Shadowlands, and this is a problem with the (bountiful) non-raid content: The raid content has a much longer shelf life than the non-raid content. How active are the Forbidden Reach & Zalarak Caverns? Completely dead. Time Rifts too, glad they finally downscaled the final boss because you'll be lucky to find 5 people doing it & I play on a High pop realm.Yes, but this was basically the model they used in WoD & Legion. The first major patch includes a small raid, then the first major patch corresponds with a second raid, even though that raid existing in the game files. 5.0 is Mogushan Valts, 5.1 is Heart of Fear, 6.0 is Highmaul, 6.1 is Blackrock Foundry, 7.0 is Emerald Nightmare, 7.1 is Nighthold etc. The only difference is Heart of Fear came out a little earlier than 5.1 because they hadn't worked out the cadence yet. As for 5.3 they later adopted the rationality that major patches should correspond with raids & 5.3 might as well been Seige of Org.
Then what exactly should they be aiming for? By the time Ruby Sanctum came out it didn't help Wrath Classic. Outdoor content that people will stop playing after a few weeks? That's why they're testing an evergreen form of outdoor content with delves (even though they went on-and-on about professions being the 4th pillar of WoW in Dragonflight with the new crafting system & that's barely different other than a FFXIV coat of paint on top.)
I suppose if they do end an expansion with a dungeon that would be a test the players respond positively but most serious players only do Mythic dungeons to prepare for Mythic raiding: You're suggesting the reverse can also be true, but since raids have roof in terms of difficulty & rewards the dynamic would be totally different.