His point, which you failed to address with your smug response, is the well-understood fact that the utility value of money falls greatly, the more money one has. The utility of 5 billion dollars is essentially zero to someone who already has a billion.

The marginal utility falls, but it's a hell of a lot more than zero.

Other than ownership of an NFL/NBA/Premier League/etc sports team, what life satisfaction or happiness improvements are unavailable to a one-billionaire?

Many people would love to own a major sports team.