(More seriously: Sure, students today might know much more maths than Newton did, but being able to learn calculus from a teacher and/or a textbook is a much lower bar than being able to invent calculus from scratch.)

True. But the average Maths PhD today is doing something Newton could never have invented at all. Yes, we do stand on the shoulders of giants nowadays, as did Newton, but picking higher-hanging fruit (say: the Standard Model compared to classical mechanics) requires both a greater knowledge of maths and a greater creative effort.

Anyway, point being, I simply don't feel able to believe that "incredibly high general intelligence" is truly the determining factor of even Famous Historical Hero-level science. There seem to be lots of other things going on.