Granted, I’ve seen one or two articles saying that AI helped find real software bugs, but what’s the ratio there, 1:500 for useful/useless AI bug reports?

It's worth distinguishing between LLM generated bug-reports submitted by randos, and developers themselves using LLMs to look for bugs in their software.

My own experience, with my own code-bases, is that the LLM I use is extremely good at finding real flaws in my code. It'll also nitpick a lot, but it has has become better at triaging issues than it used to be, so that kind of thing is easy to ignore.

Because of that, having an LLM take a look at my code before I push it has become another QC step, along with running tests, linters, and formatters. The end result is higher quality software