However, I would be remiss if I didn't question your historical claim, which seems to me a bit too strong:
> Mathematics predates the idea of formal proof by millenia [...] Formal proof only emerged early in the 20th century [...]
You seem to associate the start of "Mathematics" with Euclid, but (as far as I know) he worked at approximately the same time as Aristotle. Aristotle's syllogisms are perhaps the most famous formal logic system: their correctness relates only to their form, not their content. All deductions of the form "All X are Y, All Z are X, hence All Z are Y" are valid (assuming the premises are), regardless of the meanings of X, Y, and Z. (Outside of Greece, my understanding is that a few hundred years earlier Panini had also developed a system of formal manipulations, but for representing grammars.)
What, to my understanding, "emerged" only the 19th and 20th century was 'merely' a formal logic both expressive and sound enough to properly express modern mathematics (the Beggriffsschrift in the 19th century and FOL+ZFC in the 20th). Between Euclid and the 19th century the development of calculus was probably the biggest advance in mathematics, and my understanding is that Leibniz himself spent significant time working on formal logic.
Perhaps I have the wrong definition in mind of 'formal logic' or 'mathematics,' but I do think the history of formal logic is much more closely tied to the history of mathematics than your post makes it seem on first glance. Though I certainly agree that "mainstream mathematics" has never felt it necessary (or necessarily that useful) to express proofs in a formal logic carefully enough that they could be checked by computers; this was a fringe focus of a minority group of mathematicians and computer scientists that was co-opted as a marketing stunt into 'what mathematics is' for major corporations trying to justify their money burn.