I think there might be too much emphasis on testosterone by trans-opponents because they persistently visualize the classic masculine proportions in a drag-like feminine presentation , but not all gender-dysphorics are like that. This person below is the other extreme, and then there's all the gender-dysphorics inbetween. There is as much diversity in this group as there is in cis-genders. Just as with them, you can't monolithically describe gender-dysphorics. The only way to judge eligibility with fairness is by what a person can do and their physical ability put into the appropriate sporting class.
Picture this person thrashing sporting cis-women at 100m because they were a cis-man. Not likely, is it? I think people need to go out there, and the internet is a good resource for this, and actually look at trans-people.... the whole gamut.
It's pretty obvious to me that human gender is not binary and people can be born with mismatched personal identities to which they sense they belong. Then there's those individuals who identify with neither... they are in a state of gender equilibrium.
As iNow has already suggested the solution, it's a practical method to properly accomodate this diversity in a fair and equitable way in sporting competition.