That matches my experience as well. Having graduated from two fields at university, the most foundational knowledge came in the first two years. The third one is a deepening of the first two but can be skipped if only basis are needed. Then master degree is just playing with higher level concepts and linguo.
What would you suggest before The Art of Electronics?
Title is slightly wanky, but it's the best non-textbook beginner guide I've found, since it actually does contain all the math & theory a hobbyist will need. The explanations are very clear and most motivated people with high-school math should be able to follow along. It's not the best to read back-to-back, but has detailed explanations of lots of areas of electronics that make great primers/refreshers. I had it out last week for a quick refresher on notch filters. Doesn't go into tremendous depth, but more beginner/hobbyist friendly than Art of Electronics shich is similar (and excellent) but aimed at EEs instead of hobbyists.
For something even more beginner-oriented any of Forrest Mims' books (formerly published by Radioshack/Tandy) are great but a little dated, and don't cover anything more modern than discrete logic and don't provide much in the way of theory. Excellent introduction to electronics books though, many fun projects for getting kids into the hobby who want to dive a little deeper into electronics vs. hooking up modules to an Arduino.
Also: Handbooks. For instance, the Art of Electronics. And I recently picked up a mechanical engineering handbook, and the breadth of the topics covered at a level I can quickly understand is very refreshing. (I'm a physicist, but I mostly do mechanical engineering and technician work, with a bit of aerospace and electrical engineering and material science.)
And combined with youtube and Wikipedia, you can learn a lot very quickly.