I am still of the opinion that if a realm wants a splinter of it to be subordinate to its will, the new ruler should be a prince, a grand duke, something other than an equal rank to the originating realm's ruler.
Then there should be a option that instead of creating a new realm during the secession, we could create a Protectorate. With this we could have a different message group instead a new realm and the Leader of this could be a Prince/ess.
We can add some options to this to make it balance, but we need to make noise with this on the Feature Request.
Peace!