Side note: I keep seeing a bizarre assumption (which I can only assume is a Hollywood trope) from a lot of people here that even a merely human-level AI would automatically be awesome at dealing with software just because they're made of software. (like how humans are automatically experts in advanced genetic engineering just because we're made of DNA)

Not "just because they're made of software" - but because there are many useful things that a computer is already better than a human at (notably, vastly greater "working memory"), so a human-level AI can be expected to have those and whatever humans can do now. And a programmer who could easily do things like "check all lines of code to see if they seem like they can be used", or systematically checking from where a function could be called, or "annotating" each variable, function or class by why it exists ... all things that a human programmer could do, but that either require a lot of working memory, or are mind-numblingly boring.