I take your point. I agree that it is possible to perceive many things. I believe most human interaction with the world around them is based on multiple concurrent perceptions.
I'm saying that your perception of whether a person is probably a he or a she is more closely tied to your perception of their sex than you assume.
I encounter extremely few trans people, so the issue doesn't come up that often.
When I encounter a new person, I don't go through a formal thought process. "Are they male? Are they trans?" These are just things that I recognize.
If I encounter, say a Blaire White and don't immediately clock her as trans, it is because she passes well enough that I clock her as female. I don't believe I would be using the wrong pronouns if I refer to her as "her."
But if I ran into (another YouTuber) Rose of Dawn, I would perceive both that she is biologically male and trans. I would also use "she/her" pronouns and feel it would feel correct.
My perception is multi-faceted.
If neither "he" nor "her" feels appropriate, I'd go to gender neutral. Someone androgenous, or the person who got into it with the GameStop clerk a couple years ago, for example. the former because there are a few (rare) cases where sex and gender are both truly ambiguous, so I just don't know. The latter because, while sex is obvious, the presentation looked more like a costume (think Ogre as a cheerleader in Revenge of the Nerds) but there was no accompanying Halloween/costume party context.
There's more that goes into it than just sex.