Its not the first time I've been called Sherlock.
I just found it funny that you didn't contribute anything to the actual topic of the thread with your first post, other than reiterating what the OP said.
There's only 3 different controllers that would actually connect anyways, regardless of how many "controller types", but that is besides the point.
People really shouldn't be syncing to a game that is mid-match, unless someone is hitting the sync button on the console during the match. Unless the remotes are already paired with that system, the console will not arbitrarily add them in mid-match.
You can actually take the battery out of the Wii U Pro controller, but it is extremely cumbersome. However, if we were to come up with a way to install a on/off switch on the controller itself, it could make it easier to pair and unpair controllers. Also, the Wii U has a controller menu where you can force disconnects of controllers. This could be done at the end of a match between two players to ensure that their controllers are no longer synced.