I don't see how the hypocrisy of TERFS not caring about the inclusion of trans-men is proof of much of anything other than their own incoherence.
I don't think it's hypocrisy, nor is it incoherent.
Testosterone is a steroid that grants an athletic advantage.
When that testosterone is naturally occurring during puberty, it contributes to significant differences between male and female abilities that are extremely difficult to overcome. In some case, such as hormone suppression, it may be feasible for a sufficient amount of that difference to be mitigated to still allow for a reasonably fair competition. In other cases, it may not.
When that steroid is exogenous, it creates a previously nonexistent advantage, just as any other steroid would do.
At present, the male leagues aren't actually exclusively male, they're technically open. In reality, however, females simply are not capable of competing at the same level as males due to those biological differences. Thus, even though females are technically allowed on male leagues, they are effectively excluded by their own biology.
If a female who identifies as a transman takes exogenous testosterone, they will perform better than an unaltered female would do, and it's essentially the same as any other form or doping. Even so, it's extraordinarily unlikely that a female who identifies as a transman would gain enough athletic advantage to allow them to effectively compete against males. So they're more than welcome to give it a go, they're technically already allowed to do so.
I'll reiterated: It's about biology, not about identity.
For a comparison, consider a person who identifies as younger than they are chronologically. Would it be reasonable and coherent to allow a 40 year old person to compete against 10 year olds on a little league team, because of their identity? Or do you think that their biology as a fully developed adult with an adult athletic capability and size advantage should be held as a more significant arbiter of fairness to the children in the league?