Exactly. There's little gap between a spec that's been written to the level of detail needed and just code. There's some, but it's not a big gap after decades of umpteen new frameworks and languages and new forms of abstraction.

The core of the misunderstanding is between new builds and making changes to existing builds (where most software dev work actually happens). Yes, you'll get a great headstart with a detailed spec for a new build. The issue is in the hundreds of changes that'll follow that.

Do people think that the desire to make shortcuts and do minimum effort changes is going to stop just because you've got a bit-more-natural-language-looking spec? And then with an AI underneath making probabilistic changes to code that's now basically a compile target - they really think the dev pace isn't going to collapse, but just faster and with a big ongoing inference bill?

The LLM's do not form mental models. You are not going to get a better results from an LLM vibe coding against spec diffs vs a dev prompting it from a position of understanding the codebase and the requested change.