it's usually important to work on something your supervisor is excited about, in order to get more support.
You would fund students who are picking supervisors interested in safety, like Hutter, Steinhardt, whatever.
All of these groups are less likely to have other sources of funding compared with PhD students.
The proposal would be merely to open up 0-3 scholarships per year. So the question here is not which group is less likely to have other sources of funding, but how effective it it to fund the marginal unfunded person. There are many counts in favour of funding EA PhD students over masters students, early-career EAs and independent researchers. They require less supervision. They output material that is more academically respectable (and publishable). They are more likely to stick with AI safety as a career, ...
Overall, rank 10-30 AI safety PhD students seems comparable to these three latter groups, and clearly not much weaker.
Edited to clarify that this means researchers on longtermist econ issues.
But I am interested to know if this argument is wrong in any other respect!