What exactly would that evidence look like, for you?

It definitely increases some types of productivity (Opus one-shot a visualization that would have likely taken me at least a day to write before, for work) - although I would have never written this visualization before LLMs (because the effort was not worth it). So I guess it's Jevons Paradox in action somewhat.

In order to observe the productivity increases you need a good scale where the productivity would really matter (the same way that when a benchmark is saturated, like the AIME, it stops telling us anything useful about model improvement)