Writing does help you think... but only if you write. Dumping a bunch of stuff into a "second brain" is not you writing. Keeping a journal is you writing. Those serve similar functions, but keeping a journal is more intentional and requires you to think critically about your inputs and decide what to record and how, which is the thinking part that comes with writing. That summarization that LLMs are doing for people is removing a significant portion of the thinking, which results in a loss of capability and soundness of mind.

100%. The term "second brain" is getting kind of a bad rep because of people using the dump+AI method. I don't think Tiago Forte who, as far as I know, coined the term meant doing that, at least based on his book on the subject.

I’m in a third school: memory recall ability does not scale to meet the needs of interests and responsibilities. I’ll take all the help I can get.

I keep obsidian vaults mostly to augment recall, and often all it takes is a small cue to reveal that thing I couldn’t remember. I’ve found LLMs helpful for translating my question into search criteria - “agentic search” is magic.