I've visited the US may times, but never lived there. I do, however, have a brother who's lived there, in LA, for 25+ years. (Anything I say here is only a reflection of my experience. Please don't bash me if anything's inaccurate.)
He and his American wife divorced around 5 years ago.Their life was pretty middle class, but they had no savings to fall back on, having married and had a child late in life. Both parents have always worked full time, and their child was in a private school until the divorce.
He worked in film post-production. He's no longer working, as the effects of the writers' strike are still being felt. US welfare/benefits are very different to ours. Unemployment benefit was generous, but time-limited, to (I think) 6 months. After that, you have to work again to re-earn the entitlement. That hasn't been possible for him. The upshot of all this, is that he now lives in an RV (camper-van). His ex-wife and child live in a rented flat.
He has no health insurance, which is pretty scary in your 60s. He can't afford to visit a dentist, and has lost several teeth due to gum disease. He may be able to get help from a dental teaching hospital, but in the meantime he's unemployable in any customer facing role, as looks are so important and recruitment people won't even put him forward for interview. He has a an ok car, which he needs as he has a child to care for at weekends/school holidays, but the insurance for it is much, much higher than it would be here.
The saving grace is that he will be able to draw his state pension now, at 62, and it's around double what he'd get here, which really surprised me. (Apparently you only need to contribute for 10 years to get this, unlike the 40 years in the UK.) Once he has his pension he will be entitled to use some kind of Medicaid. In LA that pension won't go far, but if he moves he won't be able to see his child regularly.
If he lived in the UK he would probably still be unemployed, but he wouldn't have to live in an RV, as rent would be paid via benefits. He'd have free healthcare and would be able to access an NHS dentist (yes, I know that's hard in some areas).
Another signifier for me of money or lack of it is maternity leave. Whilst UK maternity leave isn't amazing, it's more generous than the US. My SIL went back to work less than 2 months after a C-section, even knowing that would be their only child. I'd guess having a reasonable amount of time off after a baby would show you have some money behind you.
I think life in the US can be wonderful if you're employed and/or have money. If not, it's a fast-track so some serious hardship. The gap between rich and poor is more obvious (to me) there than it is here.