It's really amazing how different people have completely different experiences. I work on a massive code base and I thought AI would not be able to fix anything in at least a few years since the application is very complex and does not use well known frameworks. I was very wrong. In my experience, it fixes bugs better than I could, at least given a short time budget (which is always the case, if we spend too much time on each bug we just fix bugs slower than they get reported and we'd enter a death spiral).
I have worked on this code base for more than 10 years, touched every part of it, and I wrote large chunks of most systems, despite around 20 people working on it right now. Still, when I need to figure out something, now, I often ask AI as it is absolutely wonderful in understanding and explaining code, no matter how big the code base is. My team consists of 20 very senior developers, and I am their technical lead, so I think I know what I am talking about.
A junior would require at least 6 months of guidance to become productive in our code base, unfortunately, just because it's so big and it integrates with all sorts of external services, databases etc. I do understand that saying this is not really a flex, I would've actually preferred that my code base was so good even a junior developer could be immediately productive in it, but that's sadly just not the case. But perhaps, with the help of a AI tutor, that's actually possible now?!
If you think AI is at the level of a junior developer right now, I'm afraid you're kidding yourself.
In case you're wondering: we use Claude Code.