Adding a Diff brace with stock
rubber mounts on Diff. might have a different issue.
I see the other view points of moving all the load to one point and I agree to some extent.
However, I believe the brace actually becomes a hinge point.
Meaning, that the OEM rubber bushings will now deflect even more and the inner ear bushing may not deflect as much do to it's closer proximity to hinge point.
The Ear bushings may not get a vertical deflection but more of a twisting or sideways defelction . The rear subframe bushing should still have some give and maybe too much strain and lead to an early failure, as opposed to not having the brace.
Just another way to look at things. I'm not etching this in stone.