Well if the tub walls were installed with the valve the way it is in the pic it would woble as there is nothing holding it to the wall that I can see except maybe the shower head riser. It should have been secured to the wall in 3 places. The hot and cold lines near the valve and the tub spout. There is not a whole lot you can do now unless you can take down the walls easily. As far as the gap behind the spout he should have caulked it or shortened the CPVC more then caulked it.