Even more efficient: humans do the specs and the implementation. AI has nothing to contribute to specs, and is worse at implementation than an experienced human. The process you describe, with current AIs, offers no advantages.

AI can write boilerplate code and implement simple small-scale features when given very clear and specific requests, sometimes. It’s basically an assistant to type out stuff you know exactly how to do and review. It can also make suggestions, which are sometimes informative and often wrong.