The code it writes in the first attempt is at least as buggy as a human's. So the question is more whether it is as good at spotting bugs in its own code as it is at spotting bugs in human code

I'm tempted to say "no, it isn't". But I don't have numbers to back that up

Most software used to be written in assembly language. Microsoft DOS was mostly .ASM files, for example.

That era is over, compilers are used for almost all software, eliminating entire categories of bugs.