I like making flashcards for myself for new topics that I study, in addition to notes. Of course bash as a whole will not fit on a flashcard, but breaking it into high-level topics. looking through the cards I’ve made helps when I feel the need to brush up on a topic in a general sense before diving deeper.

Despite all this, my brain is still Swiss-cheese.

Your note taking, organizing and writing will have helped you retain a lot more info for a longer period of time. It wasn't wasted effort. Still, there is a such thing as "too much". Higher degrees of success are achieved by regularly evaluating where you are in the "too little" to "too much" spectrum.