While the multiplier is less for me ( perhaps 3x or 4x ) I think the assumption that productivity gain leads to directly to more money is bit optimistic. Unless you are self employed, or run your own company, and actually get paid by results, being more efficient is seldom paid much. ( with luck you get promotion every two years or so or pay raise every year )

I have worked for too long in the field, but this year and simply thanks to the LLMs I have actually managed to get 4 usable hobby projects done ( as far as I need them to go anyway - personal tools that I use and publish but do not actively maintain unless I need some new feature ), and I have been quite productive with stack I do not normally use at our startup. Most previous years I have finished 0-1 hobby projects.

The ramp up period for new stack was much less, and while I still write some code myself, most of it at least starts as LLM output which I review and adjust to what I really want. It is bit less intellectually satisfying but a lot more efficient way to work for me. And ultimately for work at least I care more about good enough results.