I think there is a slightly different claim we’re each making, and it’s confused by the term “billion”. I think we both agree that it’s an arbitrary value that was used in the interest of an oversimplified claim above, but I think we can disambiguate the points we’re making if we generalize it.
Your statement that “it is possible to be an X-aire without exploitation of the working class” is technically correct for the value of X=billion.
But I think the claim I’m making (and the oversimplified claim that was originally made) is that: for any given point in time, in any given capitalist society, there is a value X beyond which you cannot reliably amass and retain wealth without unethical exploitation.
The post above set X at a billion, maybe it’s not a billion, maybe it’s 100 billion. 100 years ago maybe it was 100 million, and in 100 years it’ll be 100 trillion. But the point is that there exists a value beyond which ONLY exploitative practices can get you; or in other words, you will never be the richest man in our late-stage capitalist society by winning the lottery or through steady, ethical investments.