if the value of welfare scales something-like-linearly
I think this is a critically underappreciated crux! Even accepting the other parts, it’s far from obvious that the intuitive approach of scaling value linearly in the near-term and locally is indefinitely correct far out-of-distribution; simulating the same wonderful experience a billion times certainly isn’t a billion times greater than simulating it once..
I often advise doing this, albeit slightly differently—talk to their recently graduated former PhD students, who have a better perspective on what the process led to and how valuable it was in retrospect. I think similar advice plausibly applies in corresponding cases—talk to people who used to work somewhere, instead of current employees.