Yeah, this is my takeaway whenever someone uses “McMansion” in a disparaging way - it’s mostly to sneer at some “lower class”.
The people who devalue mcmansions largely do so because these houses are the material legacy this country is leaving, and it's objectively shit. They are an irresponsible way to build and organize neighborhoods.
Me, I live in a late '50s tract house and it suits me fine. I don't actually care what kinds of housing other people want to live in -- because it's none of my business. Manhattan coat closet or suburban "McMansion" -- whatever floats your boat.