Another way of phrasing what this extra layer of maintainers provides, is a second group of people who can introduce their own irresponsible, user-hostile, and potentially malicious (or at the very least, negligent) decisions. Worse, often times these developers have less (in some cases, far less) knowledge of how the code itself works, and are applying their own patches, often with minimal testing, without fully understanding the scope or impact of the changes they're making. For every poor decision you can find in a package that is popular enough to even appear in one of these downstream repositories, one could just as easily find a case where this extra layer is introducing their own problems.
The non FUD-ish answer is that whether you get your software directly from the upstream developers through an uncurated repository like PyPI, or through a curated repository like a Linux repository neither one is inherently better than the other. Each of them has a variety of pros and cons and part modern day engineering is looking at these tradeoffs and choosing the right set for your particular situation. Sometimes that will even mean that you're choosing different tradeoffs for different packages on the same system.