@simon I appreciate you writing about this, specifically because a lot of people in LLM-positive coding circles look to you for advice.
This is a key part of why many open source maintainers (myself included) have been averse to these products from the jump (reaffirmed by our interactions with people who have thrown in). We cannot faithfully execute the role of maintainer without clear understanding of tacit assumptions, limitations, and nuance of leaky abstractions. While some can be addressed through documentation and tests, PR review is an important medium in which to disseminate understanding within the community, and possibly conceptualize better approaches. The trust of the community depends on performance of these cognitive processes.
I believe the effect you describe becomes more insidious in larger projects, with distributed developer communities and bespoke domain knowledge. Such conditions are typical in research software/infrastructure (my domain), and the cost of recovering from such debt will often be intractable under public funding models (very lean; deliverables only for basic research, not maintenance and onboarding). Offloading to LLMs interferes not just with the cognitive processes of the "author", but also that of maintainers and other community members.