> Reviewers might not have relevant expertise to judge whether a paper is good or not...
Finding enough quality reviewers is hard. There are so many papers (heck, you put out 30 papers in 3 years!) and there is not much incentive to review. I review maybe 5x more papers than I write each year. It's doubly hard to get good reviews out of senior people. For this reason, I think grad student reviews are not a bad solution. In my experience, grad students puts in more effort and write decent, careful reviews. The very worst, low-effort reviews seem to come from established people who can't be bothered. A lower reviewer bar at workshops is fairly common and reasonable. Workshops are not the main publication venue (at least in my areas), so they mostly just want to filter out papers that are bad rather than only accept papers that are good.
> Politics...
I can't say too much about this since I primarily work in theory, but my perception from the outside is that the more "lab"-dominated a field is (i.e., accepted papers tend to come from some group with 20 PhD students and 10 postdocs) the more likely there are to be "mafias". Maybe this is a function of the kind of people who want to head up a lab, maybe it's a function of the kind of work that gets produced in factory environments, or maybe it's baseless prejudice from me.