Comment by giantg2

The third option is that the person who used Cursor before had some sort of skill atrophy that led to lower unassisted speed.

I think an easy measure to help identify why a slow down is happening would be to measure how much refactoring happened on the AI generated code. Often times it seems to be missing stuff like error handling, or adds in unnecessary stuff. Of course this assumes it even had a working solution in the first place.