The vast majority of authors are not represented by any publishers, and KDP is built around exactly those. The KDP limits does not affect anyone represented by larger publishers - only indies and small press (and genuine small press as opposed to imprints of larger publishers are few)

Except that's not the trade off, because the slop producers would then just create more accounts instead of uploading more books on the same account. Which is probably what they're doing even with the existing rate limit.

So all you'd be doing is inconveniencing the actual human who just wants to use one account for all their books. Of which there could easily be more than one.

Moreover, trying to justify things with ratios like that proves too much, because slop can give anything a ratio like that. They can generate trillions of books, any number. If you banned everything then you'd be banning millions of pieces of slop for every one human-authored book, but you'd also be banning every human-authored book.

What you need is the thing that minimizes false positives, because the base rate of true positives is now so high that even a negligible false positive to true positive ratio would swallow most of the real books.

It has nothing to do with hoarding. There are lots of authors who have published works using something other than Amazon, and for each one that uses Amazon there is a first time they started doing so. Amazon didn't even exist 50 years ago.