> If you have to review what the LLM wrote then there is no productivity gain.

You always have to review the code, whether it's written by another person, yourself or an AI.

I'm not sure how this translates into the loss of productivity?

Did you mean to say that the code AI generates is difficult to review? In those cases, it's the fault of the code author and not the AI.

Using AI like any other tool requires experience and skill.