I think people underestimate the frontline deployability piece regarding hormones. Prolonged loss of access to hormone therapy is rough on the person, just as losing access to any medication like ADHD medication or asthma medication would be if you're cut off from supply while fighting in the bushes.

That being said, not everyone in the military needs the same requirement. For example classes are assistive technology that a lot of people in the military use and fighter pilots have more stringent uncorrected vision requirements compared to infantry. Depending on your role, post-enlistment medication requirements do not automatically get you kicked out, though your role may have to change. In an advanced military, there are lots of non-frontline roles to fill, especially now that non-frontline drone warfare is becoming more and more prevalent. Some militaries around the world are starting to accept certain medicated conditions including mild mental health conditions. When you're understaffed, you can't afford to turn away otherwise able and willing recruits.

Militaries absolutely have to conform to the people who serve in them. User-centered design started in the military, equipment has to fit and be usable by the humans that operate them--a single standard vest size does not properly fit most people, hence adjustments. Militaries had to conform to humans when they realized humans get PTSD. Militaries had to adapt to mitigate racism as mixed-race units were ultimately the better option--no shit there was pushback on the grounds of distraction and unitncohesion. Tampons were needed when women joined. You trade-off logistical and social complexity for a bigger force and create opportunities to tap into the best of those new populations you include in your military. The US Marines have it right. Improvise, adapt, overcome, then adapt gain.

The question about trans people being mentally unwell is just misinformed. Trans people go on hormone therapy so they aren't dysphoric. They're not mentally unstable.