Yes, all these things might create entrenched groups, but make working viable in many occupations in the first place. I would take the groupthink in that case too.
If you're in a sector that isn't growing, or might even be shrinking, I imagine promotions are a lot more competitive...
Admittedly, 'reassignment' might not be the most precise term for this...
When you need to find that many trusted, competent managers that quickly, you can't afford reject people on the basis of their surname :)
But the lack of process and inexperience basically amplified the bias. There too much guess work going into decisions, so they were primary based on pattern matching like things. People were making decisions on very little information and in ambiguity, which made all the assumptions matter more. Where while bigger company I am in now, while there are people who openly express sexist opinions, in general I think I am getting more equal results.
Mostly because once they are making the decision, it is more likely to be based on my actual track record rather then feelings. Not that it is perfect, but when it is unfair, it unfair in all kind of various ways toward everyone and it seems more random. More likely based on personality conflict or something of that sort.
I've worked and consulted at a variety of companies. Of the ones that had an expectation that you do 1-2 year stints on teams, then rotate to different teams and challenges, I would describe ~100% as having a healthy workplace political culture.
Of the ones that did not have that expectation, and people typically stayed on a single team for 2 years+, I would describe ~25% as having a healthy workplace political culture.
My conclusion is that, more-so than anything else, cultivating and encouraging regular internal transfers produces healthier companies. (And that's not even broaching the documentation and repeatability benefits!)
It seems counter-intuitive, and I never would have guessed if I hadn't seen it again and again...
E.g. government and many portions of academia.
People who don't support it leave, and people who are ambivalent adopt the attitudes of their remaining colleagues.