|hard mounted (with bushings of course)?
That brace will do little-to-nothing for torsional stiffness between the trans and diff. likewise if the motor or diff move up/down, that brace probably won't do much either.
It definitely will prevent them from flexing towards or away from each other, which would also stiffen the chassis if the diff is fairly firmly mounted. Being a soft-top, this definitely could have been the driving factor for the brace.