It may be that most open source maintainers are severely underfunded, but your numbers alone don't show that, because they don't account for how much support there is from on-payroll work.

See the current top comment from Electron maintainers for instance.

"supporting open source with significant funding" (in the specific sense of transfering funds to an outside entity responsible for development) is not the only way of "supporting open source" financially. Paying your employees to develop, maintain, and contribute to it is another. I suspect it is the primary way historically for historically succesful open source (although research in this area would be helpful). It might (or might not) be the primary way even now; we don't know from these figures alone.

Employees paid to do on-the-clock work might (or might not) be sufficient to sustainably provide resources/"funding" to open source. Or there might be reasons it's unlikely to work, or unlikely to work as well going forward as it is historically.

I'm not sure straight-out donations to entities developing open source have ever historically been responsible for successful open source resourcing -- and yet we've built software empires on open source. There may be reasons this is not (or no longer) sustainable, but that doesn't necessarily mean this kind of fundraising will ever be more successful than it has been historically (not very, I think). Understanding what has worked in the past and making a case for why it no longer will would be one way to make the case. Just talking about current levels of direct donation without talking about how open source has actually been resourced/funded historically, to me is not a very persuasive case. (Then there's talking about the idea of monetizing open source with 'open core' or 'PaaS' or some combination, which I think some people think is what will save open source, rather than direct contribution. I have my doubts, but it's another possibility).

I think these are all important questions.