But if you grandfather lost all of $X, your father would not have any of $Y (based entirely on $X being an amount they got from business dealings and $Y being a smaller amount which came from $X).
Subtract it from what he would have earned if he had dumped the cash into an index fund, and we may find that his earning, creating and saving abilities were negative. His only profitable skill may have been having a father who dealt in slaves.
My father had his own earning, creating, and saving abilities.