See, in my experience those kinds of numbers are not realistic even on the face of it. I posit that it's not humanly, cognitively possible to read, properly think about, review, and really deeply understand that amount of code.
When I wrote code manually, I'm not just slower because I type slower than an LLM (barely -- I go fast when I know what to type) or I need to look stuff up. During that time, my brain is also super busy looking for and analysing edge cases, data flow, performance, potential security issues, etc.
If I go too fast, those are the kind of issues I'll find with that code days, months, or years later. If I do, the stuff lasts and saves so much time down the line. Even the best, latest, biggest models cannot write code with that amount of oversight by someone who knows the requirements, context, environments, and codebase. Even the LLM coffee I feel I reviewed carefully will have those kinds of issues, because my mindset when "orchestrating" and reviewing agent cover is fundamentally different than when I'm in the designer, architect, and builder mindset. This is also a direct consequence of the amount of code that is passing over my desk.
I'd say that for any productivity gain that exceeds 30%, maybe 50%, on production code, you're inherently going to have that kind of quality loss. It just doesn't scale that way.