I think the biggest bias here is that most donors would like to be able to point to their clear successes and the people they helped. For most folks, this leans them against x-risk because a) you’ll very likely fail to lower x-risk b) even if you succeed, you usually won’t be able to demonstrate it.
On the other hand, it’s also harder to tell if you’ve failed.
Like Ben, I doubt this kind of analysis is going to change people’s minds much one way or the other.
In practice all of these figures seriously underestimate the full impact because they don’t consider flow-through effects such as:
the people whose lives are saved will have more children themselves, perhaps resulting in hundreds of extra lives over the very long term (I know of people who have 100+ great grandchildren)
people for centuries or millennia into the future will be richer because the country developed economically sooner as a result of having healthier, better educated, and more productive people now (this is a version of ‘astronomical waste’).
If the direct impact is lower, the flow-through effects will also be lower, but ‘$3,000 per life saved’ is still very misleading as an indication of the absolute cost-effectiveness.