If any engineer sent me a 20,000 line refactor I'd immediately reject it and tell them to go back and start making changes incrementally at minimum. More likely I'd force them to have a whole design discussion with the team to make sure that what they are doing even makes sense.
What happens if they push out slop that significantly increases your infrastructure costs? What happens if they push out slop that significantly increases the number of bugs or outages? What happens if they push out slop that has no observational metrics, dashboards, or tooling?
In every case you push back on the team and make them fix their shit. I don't care if they are using LLMs or not. They are responsible for their work being sufficient quality. If they aren't meeting those standards, then they need to step it up.