That assumes that the value of a solution is linear with the amount completed. If the Pareto Principle holds (80% of effects come from 20% of causes), then not getting that critical 10+% likely has an outsized effect on the value of the solution. If I have to do the 20% of the work that's hard and important after taking what the LLM did for the remainder, I haven't gained as much because I still have to build the state machine in my head to understand the problem-space well enough to do that coding.
I personally think of AI tools as an incremental aid that enables me to focus more of my efforts on the really hard 10-20% of the problem, and get paid more to excel at doing what I do best already.