Hearing Lan Wangji say so makes him think of Claudius in Aziraphale's body -- how he could almost immediately recognize Claudius' physicality in that body's movements, Claudius' inflections in that body's voice. He thinks of watching Claudius spread out those huge white wings and how it made heat tremble through him from his face to his groin. If Claudius were confined to that body forever, Galahad wouldn't love or want him any less. Lan Wangji is right: it would no longer matter.