I completely agree. It's more than 40 years since I wrote my first program, and I've never seen software that was first specified and then written and all was good.
The most difficult part of any non-trivial engineering is understanding the problem, and the first versions of a piece of software are how you reach that understanding.
That's why I do not think that AI-powered "software factories" will ever work. It's waterfall development all over again. An architect writing UML diagrams and handing them off to the team of programmers to do the essentially mundane task of implementing... the wrong thing.
AI is, however, very good at helping you go fast from the wrong first version to the less wrong second one. But you need to remember that your main task is to understand the problem that you are trying to solve.
Yeah and any detailed design is still likely to skip over "obvious" things like "only admin users can use admin features". Both the PM and the engineering team will understand this implicitly. But with AI, you never can tell if it's going to make that inference, or just create admin users and admin APIs with no relation between them. These are also the bugs that can most easily slip through, because the reviewer wouldn't even think to look for it.