In addition to the other comments, AI has enabled drive-by contributors that do not disclose their AI use, and it either increases the maintenance burden or leads to non-trivial bugs when such code is merged without a thorough review.
I am not as biased against AI as others, so my view on this is that this is more of a social / cultural issue than any problem inherent to LLMs.
Another potential problem for FOSS is legal liability regarding licensing. I am not well versed on this so I'll leave the subject to those who can further expand on it
Your analysis reminds me of https://cendyne.dev/posts/2023-05-11-reverse-centaur-chickenization-chatgpt.html#chickenization, and I agree that there is an implicit promise of automating qualified labor away, but on the other hand, the problem is not necessarily in reducing the average labor time required for a given activity but what it means under capitalism.
Personally, while I find LLMs valuable for a certain subset of tasks I also do not think they are able to entirely replace people in their current form. This won't stop capitalists from trying, unfortunately.