“Name on building: upper class. Name on desk: middle class. Name on shirt: working class”
It’s not perfect, but the idea is that class as most people conceptualize it is determined by workplace and lifestyle affordances and isn’t a neat percentile cutoff but flexes and wanes in size.
But it captures the essence of the upper-middle split. The upper class earns income from assets. The middle and lower classes from employment.
This isn’t an economic conversation, but a political one. The upper classes are economically sovereign. The middle and lower classes are beholden to their employers, at least during the savings stage of their careers.
Put another way, a child born to an upper-middle class family gets a leg up in educational opportunities and connections. A child born to an upper-class family may never have to work at all. Their principal challenge is retaining familial relationships. Referring to the upper middle class as “upper class” papers over the exorbitant privilege the latter retains.