I don't really buy the distinction between "upper middle class" and "lower middle class" and "lower upper class" and "upper lower middle class" or whatever other variations people can dream up. These just seem like people trying to find a more granular place to stick themselves on the economic totem pole.

In my view, we have two classes: People who have to work for a living, and people who don't. Most of us are in the first class: Our wealth (net of spending) does not grow unless we are working. We're N missed paychecks away from being broke. That N may be a high number (what some people call middle class) and that N may be a low number, but everyone in this class has a similar set of problems. Yes, small-N is more difficult living than big-N, but we are more similar than different.

The second group, the people whose wealth net of spending grows without them working, live in a totally different world than the rest of us and have totally different life experiences and problems. They simple don't worry about paychecks the way the rest of us do.

So this whole "upper middle class" distinction is IMO not very important. Now, more than ever, we need class solidarity, not more labels.

It's an interesting question, we often talk of 'socioeconomic class' but in reality social and economic class are quite distinct things I think. This is particularly pronounced in countries like the UK where the social class system is very entrenched; it correlates with wealth but can be fairly independent of it, it's much more about the subculture you belong to and the way you see yourself within the world. You're born into your social class and you can't really change it within one generation no matter how much wealth you acquire.

Economic class is the more useful framing and it's exactly as you say I think, you either work to put your bread on the table or you own things that put your bread on the table for you. There's other features of economic class but that's the dominant one. This is the class difference that matters the most in my opinion when it comes to explaining aggregate motivations.

I like this framing. The differences between these two groups is much bigger than the differences within these groups, at least at some fundamental level. There is as always, nuances, and a grey area somewhere at the transition.. but overall yeah. You are either in need of some sort of income related to something you actively do, or not. There are of course ways to distinguish subgroups, but that is often as much or more culturally / socially than purely economical / financial.

What about soccer players actors that make millions and their income comes from working?

One of the things Marx got right was to analyze society in terms of economic interests, and realizing that there was an intermediate class whose interests are more linked to that of the upper class than to the interests of the masses.

In feudal times, kings and barons needed lesser gentry to carry out their plans. "Billionaires" likewise need armies of professionals to run their organizations. This group "works for a living," but that's a superficial distinction. In reality, those peoples' financial interests are strongly linked to the interests of the billionaires. There's a lot of people who "work for a living" that sent their kids to college by helping paper up deals that moved factories and jobs to China. The fact that those lawyers and accountants and bankers also "work for a living" was only a superficial similarity they shared with the factory workers whose jobs were outsourced. What dominated was the material interest--one group had skills that enabled them to benefit from globalization. And another group lacked those skills and suffered from globalization. You'll see the same from AI.

Your "class solidarity" has had the opposite effect of what you probably intend. The more the upper middle class started seeing themselves as "part of the 99%," the more they diluted the mission of organizations that advocate for working class interests.

I do think there's more class granularity than that, and it's important to understand how such distinctions can make it more or less difficult to organize and cooperate. E.g. the idea of a petit bourgeoisie is useful for understanding why small business owners, despite indeed needing to work for a living, are generally against unionization.

But the core of your point certainly stands. "Higher wage" vs "lower wage" does not make a big difference in terms of our fundamental interests, and the interests of workers are far more similar than people realize.