This has always been the argument in favour of things like materialist and capitalist philosophy - the outcomes are much better than the alternative.
There are countless well-meaning individuals who have achieved nothing, because they give their wealth away early on, compared to this one convenient counterexample in Gates, who firstly made obscene wealth with tactics that were pretty shady in my opinion, certainly anti competitive, then did flat-out more good.
If Gates were more relatively generous through his life, it is pretty plausible that he and a lot of poor people throughout in the world would be _worse off_. This is a strong argument against being relatively generous.