Another factor not brought into consideration here may be that there are two uses of "senior dev" in this conversation so far; one of them refers to a person who has been asked to work on something they're very familiar with (the same tech stack, a similar problem they've encountered etc.) whereas the other one has been asked to work on something unfamiliar.

For the second use case, I can easily see how effectively prompting a model can boost productivity. A few months ago, I had to work on implementing a Docker registry client and I had no idea where to begin, but prompting a model and then reviewing its code, and asking for corrections (such as missing pagination or parameters) allowed me to get said task done in an hour.