"""People are, in heavy LLM systems, realising that the most valuable commodity is engineers knowing WTF is going on, and that loss of understanding of your codebase is the #1 blocker to actually getting things done."""

Very much this. It is also true for non-LLM code bases. I still remember my first job at a company with a bigger codebase than my typical "university project code base". It was a full fledged ERP system and just learning the lay of the land and understanding what lives where and why took quite a bit of time.

Interestingly, I think LLMs can be used for this "self-onboarding" and codebase-browsing/understanding. I've experimented a bit with treating an LLM as a guide of a bigger codebase it has "ingested" and having dialogues about it. Works reasonably well, I'm curious if there are companies out there that use this approach.