Exactly this.
The only meaningful class distinction is working class/wealthy class.
Working class is anyone who has to work for their income whereas wealthy class is anyone whose wealth generates enough income for them on its own.
It’s possible to move from working class to wealthy class, after all people do actually do that, but it’s exceptionally rare because it’s exceptionally difficult.
Discipline alone isn’t enough, as you also have to be lucky enough to avoid things like major medical issues, bad market timing, and other financial headwinds that are out of your control.
That’s a fair point; my statement was probably too strong.
Finer grained distinctions absolutely do matter, I just think they are overshadowed by the difference between working class and wealthy class.