The pre-Jamboree camp is purely to test out equipment, and patrols, ie do the kids in the patrol mix well, is the PL and APL suited to their roles. It is also useful for the kids to get to know if they are willing to go ahead with all the responsibilities (cooking, cleaning etc) for the entire length of the Jamboree. It's not a test where a Scout leader gets to decide who's in and who's out.
Is your Scout leader going to Jamboree?
I have no advice for you Juggler as I don't really know what procedures are in place for this kind of thing, except I would possibly consider changing groups.