Maybe I'm wrong here, but I think splitting "working class", "middle class", "professional class" and other similar names is incorrect simply because of ambiguo

Maybe I'm wrong here, but I think splitting "working class", "middle class", "professional class" and other similar names is incorrect simply because of ambiguous definitions. What is even "middle"? Median middle? Average middle? By what metric? Income? Assets? Income and assets? Education? Mobility? Why are "workers" different from "professionals", who decided that? There can't be professional workers? Or is it cut simply looking at education? What about people changing professions? What about countries where higher education is "mandatory" and the system is abused? This classification is flawed by design, no wonder it's getting flawed results.