PS has been ko'd by a regular human. 😐 he is NOT invulnerable and his powers have been shown to be ltd at times. he did defeat eclipso in 1on1 battle. a very impressive feat. it's his ambiguous ROLE that dictates his inability to be destroyed, as opposed to his 'raw power'. though he does indeed have plenty of that. there is also some indication that he was a servant of the lords of light which would place him below nabu on the hierarchy. but again, there is also some evidence to the contrary as well . . .
anyway, can he defeat these 2 cosmic beings? not imo. but, in PS's case, it never serves one well to assume too much.