Regarding inflating the number of authors, it is especially bad in medicine, where I've observed a lot of names being added to papers for "political" reasons, despite the "author" playing no role in the paper.

Some journals now require an "Author Contributions" section to at least partially address this issue.

The worst part of this in the biomedical field is the conferences. Thats because sometimes you get toddlers with an advanced degree and a chair position picking the conference presenters, who will unilaterally reject or accept people on the grounds of whether they like them or see them as a competitor, even within the same department, no regards to what the poster or talk might be. At least with journals you have the editor who can sometimes mediate a hotheaded reviewer dispute in a level headed manner.

I've seen it go in the other direction too. Groups deliberately not citing other competing groups because it might help them. It's like the other groups don't exist.

I've observed this in multiple AI niches. In some cases I've emailed people saying they ignored very similar work and failed to cite it, and in at least some cases, they were apologetic and said they would update the arXiv version. Although of those times, they do that 50% of the time. Kind of tells you that the reviewers at top AI conferences themselves aren't that familiar with the breadth of the literature.

Of course they aren’t familiar with the literature. Most of the papers rediscover existing math and physics in a worse way (harmonic analysis, etc)

To be fair, there are so many publications in fields such as AI that it's really hard to stay on top of things, sometimes even within your own specific subarea. I'm not saying that to give reviewers a total pass, but I think it's reasonable that sometimes a group of reviewers might miss a relevant paper.

Yes, there are just too many publications, even with a very narrow focus. I am reminded of this article: https://slatestarcodex.com/2017/11/09/ars-longa-vita-brevis/