Your link seems to say otherwise. If economic mobility were low then most rich families would not see their wealth meaningfully eroded for generations. This was the case in feudal Europe and many ancient empires like Rome. The fact that most families lose wealth in 3 generations due to mismanagement implies someone else is gaining that lost wealth - ergo economic mobility should be high.
Personally I feel the economic mobility afforded by high paying jobs and widespread capital in the US is unmatched. I started making more money than my parents by my junior year in college and genuinely feel like I have a non-zero chance at hitting 25 million USD net worth during my life. I have friends who have gotten millions of dollars in startup funding and have 10+ paid employees. You can't say the same if you live in Europe.