Did you actually manually review the 600k lines of code?
And the reason LLMs tend to produce such insanely large codebases is partially what the comment you're replying to explained, they duplicate everything all over the place.
The codebase is large because its a complex problem and its around 75% tests. Have used various tools to find duplicates and they arent there to any significant extent.
"You are violating the DRY principle with code like <blahblah>. Look through the codebase in depth, and identify possible places to consolidate common logic."
Yeah, there's no substitute for taste, but this is not that big of a deal. I infinitely prefer repeated code to crappy, leaky abstractions. Let the model generate some slop, then tighten it up either by hand or with more prompting.
And the reason LLMs tend to produce such insanely large codebases is partially what the comment you're replying to explained, they duplicate everything all over the place.