The experienced engineer also gets an LLM though
Say experienced engineer Edna was working on a project and the new grad Nelson replaced her because he was cheaper and about as good if both have LLMs, i.e.,
Edna + LLM ≈ Nelson + LLM
even though
Edna >> Nelson.
So Edna needs to find a project to work on where LLMs don't equalize her arbitrage, i.e.,
Edna + LLM >> Nelson + LLM
and Nelson needs one where
Nelson + LLM >> LLM.
Project fails = bad.
If a bunch of projects given to NG + LLM fail, the company will say at some point "this is no good, let's not do that anymore". If they mostly succeed, they'll do it more.
From a middle manager's perspective, where they're funding 10-20 projects, this kind of measurement is feasible and carries at least some signal. So I don't agree it's difficult to measure.
If a new grad + LLM can do task X about as well as an experienced engineer can, then the experienced engineer will have to find other harder problems to solve. Personally I think labor efficiency is good; why waste your labor on easy/solved problems?