Seems to me that if you're born with functioning testicles, then you've got more testosterone circulating in your body than if you are born with non-functioning testicles, or none at all.

The testosterone will then shape a great deal of your development.

A year of testosterone suppression won't undo a body that was built while it was present. Perhaps muscle mass will decrease slightly over the year of testosterone suppression, but it is unlikely to change a person's entire skeleton.

It certainly won't shrink their hands or their feet. It won't shrink their heart. And if they've been training, even with hormone suppression, they are still going to retain a lot of their muscle mass and muscle density.

It seems to me that sport categories should not be based on gender at all. It should be based on weight categories and hormone levels, and even then I doubt it will be an even playing field between trans and cis, both in favour and against. (Trans man against cis men).