McMansion means two things at the same time. Be wary of terms like those:

1. Badly-designed and badly-built (as in, objectively not up to some verifiable standard) homes built with the look of better-built homes but none of the construction quality those homes have.

2. Houses built by the newly-rich on small lots, in contrast with the houses inherited by the old money on larger tracts of land.

The inevitable and, perhaps, deliberate conflation between the two senses is pure class warfare, of the "Established upper class striking against the newly arrived" sense.

McMansions are also non-functional buildings. It would be possible to ape the 'incremental build' style of a building that's been around for 100s of years without the aesthetic dissonance and massive space wastage of the average McManison.

If you have a different style of window in every fitting without a strong aesthetic tie then you've just raised the build and maintenance cost of the property for no reason except cargo cultism.