I think it is a bit floppy because it is a big double bearing that supports it and they are loose after it is taken apart. Mine was loose as well when it just laid in the bearing before tightening as the end of the pinion it is only supported by the little end bearing in the differential housing ..when you assemble it and torque that pinion nut up to 200+ Ft lbs it will come together tightly - the spacer between the pinion bearings gives it the critical tolerances and is matched to the bearing assembly.
Interesting, the older HO52s also had an additional spacer right behind the yoke but this was eliminated in the newer design. Check out my older post on this if you are interested,
Just my take on it. I'm no expert....
