> How do we determine that limit ?

How about a cap relative to GDP?

Elon Musk's net worth is 3% of USA's annual GDP and 1% of global GDP.

I'm not a fan of limiting wealth among the upper class. But I am a fan of stopping a small number of individuals from controlling a significant percent of the world's GDP because if that trend continues, we'll end up with individual people more powerful than the governments that are supposed to keep them in check.