Well, it's not quite that easy because someone still has to test the agent's output and make sure it works as expected, which it often doesn't. In many cases, they still need to read the code and make sure that it does what it's supposed to do. Or they may need to spend time coming up with an effective prompt, which can be harder than it sounds for complicated projects where models will fail if you ask them to implement a feature without giving them detailed guidance on how to do so.
Definitely, but that's kind of my point: the maintainers are still going to be way better at all of that than some random contributor who just wants a feature, vibe codes it, and barely tests it. The maintainers already know the codebase, they understand the implications of changes, and they can write much better plans for the agent to follow, which they can verify against. Having a great plan written down that you can verify against drastically lowers the risk of LLM-generated code