Which part is not true?
If they are confident battery is safe with moving around spacers, they don't need 120+ lbs steel box.
As long as there is a steel box, it is not a permanent fix.
Steel box dead weight is almost equivalent to one paid pax.
Are you sure you are not quoting the added weight for the two boxes. I can't see one box (plus the vent mod) being 120lbs.
Saying that the box is not a permanent fix is like saying any post production in-service mod is not a permanent fix.
In addition, part of the post mod fix was to alter the operational procedures to ensure the battery is not 'stressed' beyond its limits. Its, discharge limits were changed too.