The problem is simple: The kind of person who can understand Calc 3 enough to teach it, cannot possibly know what it is like to be the average student in the Ca

The problem is simple: The kind of person who can understand Calc 3 enough to teach it, cannot possibly know what it is like to be the average student in the Calc 3 class who don't magically just "get" it like someone who became a math professor definitely did. Teaching is a really difficult skill that most people are not born with. If you can easily understand high level math, you usually aren't going to decide to spend your life teaching, rather than making good money. The best math professor I ever had in college was an adjunct from the local community college, because they were a teacher first, and a mathematician second.