> It's reasonable to assume that anything newer hasn't been tested to that point yet, so they still have a lot of work to do on the things we haven't seen yet.
I disagree on that part - I do not think that is reasonable. If I read correctly, your assumption is that pipeline for everything is: Develop > Test internally > polish > public testing > fix.
It's also reasonable to assume that not everything needs to be tested by the public, and only those deemed to require public testing were included in public previews.
There a lot of reasons to release 'old' code, especially on a large codebase. It's not that they intentionally send out "buggy releases while sitting on a build that works", but gating is complicated business.
