The usual American idea of “middle class” is mostly (thoufh it tends to be defined more by income than actual means of relating to the economy) a mix of the upper income segment of the primarily labor-dependent class (working class/proletariat) and the lower (comparatively) income segment of the mixed labor/capital-dependent class (petit bourgeoisie).

The middle class (petit bourgeoisie) is real, but its not centered around middle income (it is middle in the sense of being between the dominantly capital-dependent class and the dominantly labor-dependent class, primarily in how it relates to the economy, but in practice also on average, in income and wealth, but it is still an elite minority, just less so than the haut bourgeoisie that sits at the top.)