As an engineer this has been my experience too. It's great to quickly get started and move through mundane things but you eventually hit a roadblock. Even knowing how the code works, it still sometimes feels like trying to fix something in a legacy codebase.
Honest reflections from coding with AI so far as a non-engineer: It can get you 70% of the way there, but that last 30% is frustrating. It keeps taking one step forward and two steps backward. If I knew how the code worked I could probably fix it myself.