her being trans seemed to have been caused by the metacrisis. It felt like it flew in the face of the normalisation. The reading in the episode is Rose is only trans because of that timelord DNA influence.

I didn't get that at all from the episode. Where are you getting that from?

Rose is trans because that's who she is. The metacrisis was a part of her up until she and Donna released it - which they couldn't do while Donna was still psychic locked. And afterward she was basically the same, only without that metacrisis energy, which didn't change who she was, it only had subtle subliminal influences that manifested in her stuffed creatures and maybe nudged her in tiny ways, but didn't overtake her.