the problem with making chihiro trans (outside of it being a vehicle for vehement sjw-types to cry transphobia on those that disagree) is that is erases the main issue that was the whole point of chihiro's character: sexism and gender roles in japan. weak = female strong = male and how it was easier for chihiro, as a weak male, to pass himself as female so that he didn't get picked on.

because it ties into gender roles, it's easy to see how people can grasp and say that he's trans, but the text does a pretty solid job of trying to make the real issue clear - he plans on telling everyone he's male, he's realized that "strength" and "weakness" are more relative than concrete, etc. By making it a trans issue, essentially they are ignoring the underlying japanese social issue and pushing a set of western values on a non-western situation. it's not so much transphobic or shying away from the issue of being trans that chihiro is cis, but rather addressing a completely different issue that gets ignored when people insist he is.