There’s a massive difference between “using AI to write code” and refactoring almost 15k lines in a single push.

The “best” uses of AI in coding are for small blocks. You don’t just tell it “I need a program that does X, Y, and Z” because that will (at best) result in horrible code. Instead, it’s best practice to use it for small blocks of code, where you tell it something more akin to “I need a function that takes {a} as a variable, does {thing}, and outputs {x}.” That way you’re not using it to generate giant swaths of code all at once, you’re just using it to generate individual functions that you can then use as needed.

But it also means that the “most skilled” (as you put it) programmers are basically putting themselves in a permanent debugging seat instead of working as a developer. And in many cases, debugging code can be just as (or more) difficult than writing the initial code. It’s also why senior devs exist to audit code from junior devs, because it’s assumed that junior devs will inevitably make mistakes that need debugging, or will make code that clashes with code from other junior devs. And it’s the senior dev’s job to ensure that the code is both functional and integrated properly.

And this “adding 15k lines of code and ripping out 10k lines” push smells a lot like the former “write me a program to do {thing}” usage.

Most skilled engineers, and even mildly skilled engineers don't use slopgenerators to write code. Some of them use it sometimes to do some menial tasks, although I'm not convinced it actually saves them time. It sure doesn't every time we measure it.
There is however a plague of low skilled people who convinced themselves that they've found a shortcut to being an engineer. Those people are producing bad things at a fast pace, and the only reason we're not in an unsolvable crisis yet is that their slop isn't hitting prod very often on account of being bad.