denounce the visage and tear off the mask

Acropolis Museum

François-André Vincent, Alcibiade recevant les leçons de Socrate (detail)

ab. 1600 Anonym, Netherlands - Portrait of a woman

For example: Beowulf does not follow the hero's journey. I have a pet theory that Beowulf is three or four stories that kind of got mashed together since it's a collection of a couple vignettes about this warrior's life and the dragon episode is rather disconnected from Grendel (unless you're John Gardner, who ties it all together in his novel Grendel). Beowulf emerges as a full-blown hero when he enters the narrative, does not have a mentor, does not refuse the call (and rather wholeheartedly embraces it in fact - "Not only am I gonna slay your monster, I'm gonna slay your monster with my ass hanging out to show off"), does not live in the normal world at any point. One could argue he returns with the elixir to his home, given that the later story has him as a king, but the story's not interested in explaining much about how that happened and keeps going after the hero's journey would claim it should end, instead jumping to Beowulf's noble sacrificial death. You really have to squeeze to fit Beowulf into that framework, and by the point where it does, you've lost all semblance of a common structure the monomyth claims to represent. Arguably, the Iliad doesn't it either, given the scope of the story is a lot smaller than some people seem to believe.

Like I get the point that the original post was making about the western canon being so heavy with authors from the US and western Europe and not caring much about works from cultures beyond that, but I feel it's worth noting that even if you grade Campbell's ideas on the most generous possible curve, they don't hold up.

And even if we pretend they did, he never intended them as a writing guide. They were only popularized as one when George Lucas took that structure and adapted it to Star Wars.