Another data point suggesting a vetting bottleneck is Open Phil’s recent shift in how they’re funding EA meta/community organizations, including those who work on long-termist causes. This was motivated in part by “high uncertainty about how to set the right grant amounts for these organizations and our sense that we aren’t providing the level of accountability, oversight and vetting that we ideally would like to. We believe that individual donors (particularly to these organizations) sometimes seem to think our investigations into the organizations in question have been deeper than is actually the case.” (emphasis added/shifted)
In other words the funder with the most incentives, capabilities, and resources to vet these organizations (which I’d guess are abnormally hard to vet) doesn’t think it’s doing enough vetting, and is worried other donors are also under-vetting (based on erroneous assumptions). And it’s not just small projects that are under-vetted, the problem seems much broader.
Re: my comment about smaller projects being undervetted, I should note the level of detail provided in the last grant report from the Long Term Future EA Fund looks like a substantial step forward, “raising the bar on the amount of detail given in grant explanations.”