Agree.

We have a bunch of tools - specs, code, tests. All of these really are models of the end outcome we're trying to capture.

You could just build something, see if you're right and then build it again. If that seems ridiculous, what makes a spec special that it can work first time?

Why we've not done this historically is code is annoying and (was) relatively expensive. You can rough out a spec document and get feedback from a wide variety of stakeholders -- after all, they can all read a document.

If you can use AI to explore a problem space and get feedback directly, that's definitely a whole new tool in the kit.