MSFT is up 18x during that time and the S&P 500 is up 5x during that time. His investments are some mixture of MSFT and other things, so we might say he would have been up around 10x if he'd given no money away.

Since his net worth is only up 3x, that means he gave away about 70% of his wealth.

The end goal isn't for him to be poor-ish but to do something supposedly useful with the money he has today.

Maybe it’ll triple again and he’ll throw in a cure for cancer(s) or Alzheimer’s.

It's part of the strategy. He endowed a giant philanthropic org. You can leverage an endowment by investing it aggressively and spending the proceeds to keep the fund running indefinitely. What he is now announcing is a pivot to start spending principal so the endowment starts to shrink until it hits zero.

Same thing happened to Buffet.

It seems weird to write this, but:

In the billionaire’s defense, he probably didn’t plan on us as a society deciding to shoveling money at his class as quickly as we possibly could.

Did it triple because the assets he owns tripled in value?