What will happen is that the automated agents (LLM or otherwise) will also be tasked with simplifying and improving performance. That’s just another part of development that human developers do automatically before they even commit, and the LLM generators haven’t been asked to do yet.
In the future we will have opportunities to ship 10-1000x faster code than the baseline competition, just by understanding the tech stack, the codebase and knowing what is not needed, and that will be an immensely competitive advantage pushing the value of such devs through the roof in the markets that value it.
If you thought no-code app builders were producing slow stuff, wait until software purely developed by AI starts to hit the shelves.
If consumers show a strong preference for Y then market forces will drive demand up for these devs, and you might want to change product strategy to compete against Y.
Of course it remains to be seen what real world effect all of this could have. I'm still bullish on the importance of human-in-the-loop patterns despite future AI progress.