We cannot infer from knowing it’s a fat-tailed distribution who’s going to be in the impactful fat tail and who’s gonna be average (or do I misunderstand you here?). We need lots of people making informed bets, and we likely need an ecosystem. We can however give recommendations based on some heuristic—e.g., if you have an easy time taking advanced ML classes, you’re more likely to have an impact in a technical field than someone who hasn’t—those are cheap tests. I recommend applying to speak with 80,000 hours advising team if you haven’t!
I think it’s reasonable to use past numbers as heuristic for future hires. I agree many impactful opportunities will be outside of EA orgs, but my hunch is most people who’ll be very impactful in those roles (e.g. as a civil servant) would’ve also been quite successful inside an EA org (depending on different levels of “absorbency” between those at a given time—see Joey’s post), depending on personal fit. Another consideration is how abundant funding in that cause is—does everything that’s reasonable get a grant anyways, or are the competitive? Again, it’ll matter if you want to do cross-cause comparison.
I wonder why this particular question that you want answers to seems to be your crux, however—it seems the most urgent question for you is which major to choose, and for that, dentistry doesn’t seem like the strongest earning to give option for the vast majority of people (or even a decision you could delay by 4 years?) - I’d encourage you to brainstorm more options and choose paths that allow you to learn more about your skill set as well as staying flexible—employment is likely going to look quite different in 4 years.
I agree with most of your points except “this is small potatoes”. Caroline is the protagonist of The Altruists coming out in November, which will likely get lots of eyes on what she’s doing now. If the series completely flops, I’d agree.