Perhaps I'm too much of a child to understand your point, but this seems like a straw man.
I think the original contention was that MCU content is low quality (and no one has provided anything to support that claim beyond hand wavey "it's for children" nonsense). The other contention was that MCU films reduce the quality of the cinema industry overall, which is a similarly baseless claim.
Independent films still exist. Dramatic films still exist. Artistic production still exists. I haven't seen stats, but I would be shocked if the market for such content is smaller now than it was in 2008.
There's the possible claim that MCU sucks the oxygen out of the room for more artistic productions. I think the idea is that the world would be better if popular content didn't exist, so that we'd all have only "artistic" content available. I think that is a world in which fewer people watch movies at all, not a world in which everyone is driven to only appreciate high art. Thus the claims that MCU reduce the quality of cinema overall seems hard to defend.
I'm curious about the other perspective, so any perspective or analysis that better explains the thinking would be helpful. Otherwise I have to assume folks are just coming up with stories to justify their elitism.
BTW: "theme, meaning, film making craft, and artistic merit"
- craft was addressed in all of the sub-categories listed: performance, visual art, music, audio, effects
- theme/meaning: varies by film (because they aren't all the same). Sometimes it's loss and grief. Sometime's it's managing conflicts. Sometimes its reckoning with the inherent conflicts in heroism. Sometimes it's displacement after war. Sometimes it's about the forces that drive people to extremism. IDK humans aren't that complicated.
- artistic merit: a bullshit concept and I think you know it. Literal urinals have artistic merit. Canvases painted red have artistic merit. "Artistic merit" is elitism in distilled form.
Edit: I will concede that the performances in "Black Widow" were particularly weak.