About to fall asleep, but, corruption affecting shape makes sense to me because when Gems are poofed, they usually come back with only minor alterations from baseline (see also Amethyst's unsuccessful attempts to go further from it), which suggests that their appearance updates like Names in the Speech (Young Wizards) and thus necessarily follows from their self-conception (see also how Garnet, Amethyst and Pearl have no stars on their outfits in any pre-Steven flashback). If a Gem's mind can't retain a full sense of self, it can't project that self.

And fusion limbs indicating emotional stability and health.