Billionaires not being probably happy or sane does not mean that there isn't a decent goldilocks zone in the middle where you have enough money to basically be comfortable and content.that is a strawman, a billionaire will never be in a position to make that choice.
The point is this - people don't "need" anything beyond survival needs and data indicates that more wealth does not bring more happiness. That billionaire is not happier because she has a different choice on luxury.
Your argument is that at some point it is enough, but that is a fundamentally flawed argument and billionaires feel a "need" more money for the things they want to the same degree that the poor or working class feel a "need" for additional things they want.
At the end of the day there is no "need" for a second jet and no "need" for electricity and neither of those things will make you happier just because you have them.