Pre AI a developer would come out of a product meeting knowing at a high level of what to build. Maybe a few key bullet points get written up in an issue tracker somewhere, but beyond that there's no additional design phase, highly detailed specifications curation, prompting, planning back and forth with an agent etc. A good dev has an intimate pre-existing understanding of the codebase, and immediately can just move to the actual implementation (writing code). The plan is in their head, and can go directly to code. And there's no huge agent written code diff to review at the end, and any manual testing happened along the way as code was manually written.
And FWIW, I'm not arguing against a productivity boost. I've tried the tools. But for me, it was nowhere near 10x, especially when working through a brand new feature or module. Maybe 2x, 3x? Though even that seems generous in some cases. And you give up a lot to get that boost with changing the way you work.
Agreed it's higher and probably closer to a 5x-10x for some boilerplate copy/paste duplication or extension of an already existing feature.