(I suspect some very junior jobs have genuinely been taken by AI, but it seems to me that the driving factor is still a return-to-mean after ZIRP).

Data scientist is an exception based on title, but in my experience there are a large number of people with that title who have never heard of the scientific method, let alone could apply it with any rigor.

I'm sure LLMs are taking some of these jobs, but a lot of the decrease is probably due to general cutbacks on overhead and a realization that they produce limited value.

It is hard to tell what is really going on. No company will admit that they are firing, e.g., DEI hires from 2023. I have seen some open source CoC loudmouths being fired, but that is not enough to establish a large trend.