I was a teaching assistant at UC Santa Barbara for 3 years, I can tell you, students might slug through the calculations , but none -- or a precious few -- really get the big picture.

Mostly, it is that calculus pedagogy is a disaster. And it hasn't been updated to include recent advances in technology (such as Data Science)

Strang is an amazing lecturer. I can tell you, that far into your Masters and PhD these same basic issues resurface. There's at least one project I can think of where the entire problem hinges on taking one derivative.