In my experience that exact order of steps I cited above is what I must do to get the vanilla GNOME desktop consistently across users on a system. I have a 19.10 home PC that I share with my wife and while my user sessions work as expected, her login screen, apps, etc. are a mishmash of Yaru light and GNOME styles. She even managed to get into high contrast mode by accident, I should get her to test for me 
It’s because of that strange development that I started looking into the issue more systematically and was surprised I needed to do that exact order of operations.
I agree that the Yaru theme looks great (
that startup sound!) and I think the default GNOME for Ubuntu makes sense for a lot of people, I just personally prefer the stock GNOME look. I guess I may be a bit beige. So far 20.04 looks really good overall, Kubuntu and Lubuntu look better than last I checked 'em out as well.
I will try and see what I can learn on the bug tracker. Thanks!