That'd be a much harder question to answer; my talent is specialized toward figuring out the shape of the right theorem to be proved, not the actual proof which is where most modern math concentrates its prestige. (This is an objectively verifiable form of mathematical talent; it means that sometimes Marcello would prove something and I would look at it and say, "That doesn't look right" and at least half the time there'd be a mistake.) I feel insecure about not being an expert in the tools by which most modern mathematicians measure basic competence; I can also apparently make "well, if that's your problem, try transforming it this way" suggestions to someone doing graduate mathematical research at Yale that are accepted as brilliant. I confidently depose that, even taking unusual talents into account, I am not in the literal top tier of mathematical potential - if I can explain basic Bayes better than anyone or was first to state the Lob problem or invented TDT, those outputs drew on at least some non-mathematical high-percentile sections of my brain (explanatory ability in the first case, or what's somewhat vaguely referred to as "philosophical" talent in the other two). I'm also reasonably confident that, given a hundred modern mathematicians, an average of zero will pick the right problem to solve.

I think I'm comfortable at this point with saying that I'm in the top 99+% of writers - I've been picking up "real" books and trying to read them and finding that they seem visibly badly-written to me now that I've written HPMOR. Though I'm still not in the literal top tier; there are basic things in writing that I still don't do too well, despite being outstanding in others, and my new level of skill is just enough to start noticing that Neil Gaiman and Terry Pratchett are doing things way the hell above me.