The thing you're really failing to consider is that, at least in the UK, 95% of transwomen have not undergone any kind of medical therapy and 80% are expected to never do so.
We should be accurate about the concepts of sex and gender. Sex is the biological characteristic resulting from a certain pathway having been taken in the development of the fetus, consisting of primary and secondary sex characteristics. Gender is a social construct consisting of a behavioural stereotype (men are violent, women are submissive, men are logical, women are emotional, etc etc) and a social force which acts so as to force people into those stereotypes. Gender is hence always relative to a certain society, whereas sex is biological.
What is relevant for sports is secondary sex characteristics (lung capacity, muscle mass, etc) so what's relevant here is trans-sexualism and not trans-genderism. I don't see why there should be an expectation why someone with measurable sex-based advantages should be allowed into competitive sports of the other sex, whilst having no intention to do something about that advantage, for no other reason than that it "feels like the right thing" to that individual.
Trans-genderism is a category error anyway, confusing gender (a social construct) with personality (an individual construct).