There are some European countries with worse mobility than US, but the top countries on most indices I've seen are mostly European, and the US is a ways down.

I see the study posted above but I seriously doubt this and think there’s some statistical nuance being lost here. Looking at a list of the worlds richest people outside of the US most of it is entirely inter generational while the US citizens shot from middle class to billionaires thanks to tech and what not. The income disparity alone means it’s gonna be hard to argue against US citizens having a better chance at building wealth than Europeans and median/average wealth in the US vs the biggest European countries confirms this.

Sort of depends where you are. I was working in the UK and moved to the USA and my earnings and lifestyle shot up. The USA is very variable depending on the state you are in. The studies mentioned may not properly account for that variability.