The best-known US institutions -- Harvard, MIT, Stanford, etc. -- are riding based on having been fantastic institutions in the sixties, eighties, nineties, and even early 00's. I think it will be decades before reputation catches reality, but at some point, it will happen.
It turns out massive endowments and fundraising didn't make schools better; they misaligned incentives, brought in the wrong types of people into leadership positions, brought in conflicts-of-interest, and led to all sorts of corruption.
The second-tier seem to still be doing okay -- the WPIs, Georgia Techs, state schools, and so on -- but the elites populate their faculty ranks, and you can see culture slowly creeping in.
More money doesn't always make things better. Go figure.
TL;DR: If you went to top-20 school, and you're asked for donations, donate to a local state school, an HBCU, an educational not-for-profit doing good work in your community, or elsewhere.