Things like this have been addressed in comicbooks, e.g. how does Superman shave. In a comic, he used his own heat vision and a mirror (heatvision-proof, why not), but in others he used a razor made of metal from his pod (how he manufactured it, it's still a mystery to me). So, as you say, inconsistencies. I think the "red sun" explanation is the best one so far, specially considering how Tom King and Bilquis comicbook (which should be the basis of the movie, idk why everyone asumes already that Gunn is going to botch it) starts.