> a certain degree of "productive struggle" is essential

Honestly, I'm not sure this would account for most of the difficulty in learning. In my experience most of the difficulty involved in learning something involved a few missing pieces of insight. It often took longer to understand the few missing pieces than the rest of the topic. If they are accurate enough, LLMs are great for getting yourself unstuck and keep yourself moving. Although it has always been a part of the learning experience, I'm not sure frantically looking through hundreds of explanations for a missing detail is a better use of one's time than to dig deeper in the time you save.