I feel as though this analysis only makes sense in hindsight; in the past, when people used to say using books as a way to store knowledge outside your brain would make a similar argument, but would add a fourth pillar of memorization. Even now, a lot of people in different professions (such as law, and medicine) still absolutely drill memorization as the first step in building a strong knowledge base before getting into more practical, day-to-day used information. When people are forced to memorize a large amount of things in a cohesive subject, it forces your brain to make connections between ideas out of necessity to keep the information in your head. This definitely has an effect on metacognition and practice. So I wouldn't argree with you that the analogy with books=brain rot isn't valid.