Why?
If the engineers thought those weren't important they would have not fitted them in the first place. Car companies go way out of their way to save 5 cents a car wherever they can.
You are correct. The backing plate is on the outside of the spindle in this case. It's been a long time since I had one torn down. In any event his backing plates are not visible and that put up a red flag for me. I also agree with your take regarding bearing race or rotor issues.
My BJ74 has...
Those calipers are not supposed to be split open. I would not use them, but that's just me.
Maybe the rotors are improperly machined or are not seated fully on the hubs or are mis-identified.
If you still have the old rotors you could mount one up to see where it sits in relation to the caliper.