In my experience AI can write _something_ from scratch, but often edge cases won't be handled until I go through and read the results or test it. Usually when I'm writing by hand I will naturally find the majority of edge cases as I go. By the time I've read through the results and fixed said edge cases, I usually would have been faster just doing it myself.
This has been my experience thus far. Yes, a complete prototype can be made, but.. you don't really know until you read the code and test it. Just yesterday, small things came up in terms of Qt screen focus that wouldn't have come up otherwise save for initial testing.
I think, and I recognize it is mostly against the 'agentic' push, I will stick with slow iteration.
My experience is the opposite: AI takes too many edge cases into account and guard against even the most unlikely thing. The upside is that it often handles edge cases that I either didn't think about or was too lazy to implement.
I can with full confidence say that the code AI writes is more robust and safe than if I would have done it myself. The code definitely becomes more bloated though.
My experience has been that it wraps all the obvious things, and even some obscure things, in error handling. In this sense it is safer.
It also fails to write abstractions unless they're carbon copies of a well established pattern, and when abstractions already exist, it needs babysitting to ensure it will use them appropriately. It won't introspect about its current direction unless forced to by the user or by an error, and when forced it will happily "fix" non-issues just because you pointed them out, since it's a happy little yes-man.
Because of this, code written by a good engineer is more likely to start out broken but converges towards correctness as more abstractions get built, while code written by AI duplicates abstraction layers, leaks between them, and never converges towards anything.
I've definitely had a lot of these same experiences (in fact I've been fighting it on one particular issue the past couple of days and I'm pretty much just giving up and going back to solving it manually now).
But it still seems to get it right (or at least close enough to right that I keep using it) more often than it gets into these traps.
It also loves to add edge case handling where it's not needed and in poorly chosen places