Ever read books in the Bobiverse? They provide an pretty functional cognitive model for how human interfaces with tooling like AI will probably work (even though it is fiction) -- lower level actions are pushed into autonomous regions until a certain deviancy threshold is achieved. Much like breathing -- you don't typically think about breathing until it becomes a problem (choking, underwater, etc.) and then it very much hits the high level of the brain.

What is reported as cognitive decline in the paper might very well be cognitive decline. It could also be alternative routing focused on higher abstractions, which we interpret as cognitive decline because the effect is new.

I share your concern, for the record, that people become too attached to LLMs for generation of creative work. However, I will say it can absolutely be used to unblock and push more through. The quality versus quantity balance definitely needs consideration (which I think they are actually capturing vs. cognitive decline) -- the real question to me is whether an individual's production possibility frontier is increased (which means more value per person -- a win!), partially negative in impact (use with caution), or decreased overall (a major loss). Cognitive decline points to the latter.