Or referring more to the process of building the specs, requirements engineer(ing). Imho agile became a way of hand waving most of this critical process and responsibility, in place of a new inefficient and ill-defined process.

Yes, you don’t know the nuances of all specs upfront and revision will be necessary. Turning the ship with arbitrary degrees of freedom outside of bullet points on a roadmap is not an efficient way to resolve that for many projects.