> occasionally repeating myth as fact.

I'd be very surprised if that didn't continue to be true. I saw one that asserted that the American middle class didn't emerge until the 1930s.

(The middle class was well established by the time of the American Revolution.)

Definition of what constitutes a middle class is so vague that it's birthtime could be placed anywhere in the timeline just as well. I don't understand what a middle class is. Someone is either able to live off their property/investment then they are rich, or not then they are poor. Is the middle class someone who still can't, but has a reasonable chance to get there within their lifetime? Only viable definition i can think of.

A simple answer is people who own middle class homes. Shopkeepers, farmers, etc., are all middle class. America was full of them before 1776.

Yes, but what about a non-tautological definition - "The middle class is the people who own middle class homes" raises the question "What's a middle class home?". The answer of course is "A middle class home is the type of home typically owned by middle class people".

It gets harder to define something with an answer more explanatory than "that thing is that thing".

Define it as you please.

You can see plenty of them in painting from before the Civil War and photographs afterwards.

This, plus obsession with owning a home is usually a sign of poverty.