Where does that info come from? I went to school with people whose wealth can be traced back more than 20 generations. They didn't seem to getting poorer.

"The richest families in Florence in 1427 are still the richest families in Florence"

https://qz.com/694340/the-richest-families-in-florence-in-14...

Here is some data showing 70% by the second generation and 90% by the third:

https://www.google.com/amp/amp.timeinc.net/time/money/392530...

Perhaps you just met some of the exceptions.

Do you have data that isn't a blatant ad campaign consisting of pithy statements from a wealth management company trying to scare people into letting them manage their money?

Exactly this. It's extremely difficult to lose your money at that stage.

Something like 65% of all land in the UK is owned by the same families that owned it in the Norman conquest. 0.3% of the population today. Since 1066-1100.

The stat you quote may apply to some broader definition of “wealthy”, but for the true 0.1% - 0.01% it is truly eternal, and accelerating.