Not OP but I could see some shops pushing AI generated code to production, then when changes need to be made, they can't get the AI to modify the existing code in just the way they need, so a human has to intervene.
I can't get Copilot to generate Python that adds numbers together correctly sometimes. Getting an LLM to generate correct, working code for a language that hardly anybody writes anymore is almost assuredly going to lead to failure.
The slope doesn't really matter, because the target is "better than a human, and able to identify and fix its own errors". The slope will decrease as you approach this threshold.
It's also wildly bad to plan to train and fine tune on code that you know has bugs. Already we have Copilot generating code with trivial vulnerabilities because that's what it's trained on.