It sounds like that's an area of study that's not completely clear, but that height and muscle mass seem to be retained advantages.

http://fightmedicine.net/uncategorized/a-medical-and-scienti...

>The effects of hormonal therapy over time, in this case testosterone deprivation and estrogen supplementation, are not completely understood. However, what is clear is that transgender individuals that underwent surgery after puberty will retain some male features, such as increased height. Male–>Female transgender patients tend to retain more muscle mass than female–>male transgender patients gain, suggesting that some gender-specific attributes remain. Whether effects such as height will prove beneficial in MMA like they do in other sports such as basketball remains to be seen. Another question is if the fighter is completely transgendered. Taking estrogens without castration will leak out testosterone that can maintain muscle mass. Furthermore, how much estrogen is being taken? If it’s not enough, then muscle strength can be closer to male levels

> Furthermore, how much estrogen is being taken? If it’s not enough, then muscle strength can be closer to male levels

But this is something that can be measured and has less to do with the fact that the HRT happened after puberty.

Our bodies are a hell of a lot more complicated than just adding some hormones here and blocking some hormones there.

That may be, but at the same time I would think there are only a limited amount of things that would affect your performance in the ring, at least to a significant effect.

Bone density for one

How important is bone density though? Do we measure bone density of males, and exclude those who hit the genetic lottery and have super high bone density?

In the male league, do some fighters get to refuse to fight others based on bone density differences? I'm thinking not, which is why this restriction seems artificial, sort of like grasping for straws to find a difference (though I'm open to being proven wrong).