The hard class teaches you how to learn. The easy class just teaches you the material.

A class that beats you teaches a second subject underneath the first one. Once the material stops going in from a single read, you are forced to find out how you actually learn: what notes do, what practice does, when to ask. The easy class never raises that question, so the content arrives and the method does not.

In whichever subject is currently beating you, keep track of what works instead of just grinding. Try one new method for two weeks and test it on something real. Whatever you find out will be worth more later than the content of the course.