I cant follow you there. I know Ballentine pretty well and what he shows is based on the invarience of probabilities the dynamics follows.It is in those correspondence rules that the problem arises, and depending on how one interprets the Born rule, for instance, you might have a smaller or bigger problem.
What do you mean by devised? Historically - probably - but so? We now know it follows from much more general considerations having nothing to do with particles eg Gleason's theorem.I would say the Born rule was devised having the particle picture of classical mechanics in mind. Don't you?