I was fortunate that my K-12 math curriculum included proofs and derivations. We learned about sets in first grade. This was a suburban public school using textbooks from a mainstream publisher, in the 70s. Likewise college physics. As a result, there was no transition, and my college math grades went up when the courses were primarily about proofs.

It seems like a couple of things have happened since then, good and bad. What constitutes "math" has been reformulated to give kids a better chance of learning it. In my generation, we did proofs, but it was OK if 90% of the students failed to learn math at all. Math has multiple roles in society, as do science and computer programming, and preparing kids for professional careers in those subjects is not the only reason to teach them.

On the other hand, "math" has also been reformulated to manipulate standardized test scores.