Class and income are related but distinct. People with advanced degrees and high-autonomy white collar jobs ("upper middle class") are a distinct sociological cohort from people in the trades.

You may think this is bullshit, but class has some decent explanatory power for otherwise-puzzling observations, like how the children of the first cohort defy their own economic incentives to avoid the behaviors of the second.

It offends modern liberal sensibilities to treat class hierarchy as normative ("classism"), but most acknowledge its existence and utility as a descriptive concept, one which is a lot more nuanced than bands on the income spectrum.