This is surely wrong.
Yes, there may sometimes be a reason to allow a vendor change. But in that case, “zypper” will normally present a conflict resolution message where a vendor switch is one of the options.
What you are doing may be working well for you, with your particular choice of repo priorities and repos. However, we regularly see forum posts from users with a mess of repos that will cause problems if they follow your advice.
Nope. This happened e.g. when Mesa packages were moved from openSUSE to packman.
I discussed this issue at length since five years: Search results for 'zypper dup priorities @karlmistelberger order:latest' - openSUSE Forums Users with a mess of repos indeed experience problems because they ignore my advice.
To be honest, most of your solutions for your infamous hosts are no real world solutions for normal users. No offense intented…
Mesa packages were never moved. You apparently do not even understand why Packman exists.
The discussion is becoming repetitive. Time to close the thread.