Specifically on your ADHD point, while symptoms vary in intensity, refusing to medicate someone because you perceive their symtpoms as mild ignores the herculean effort many unmedicated kids go through to keep up with their classes. How many unmedicated ADHD kids burn out in highschool or college when they just can't overpower their natural brain processes to conform to the rigidity of modern life any longer? How many would have a much greater chance of success if they weren't weighed down by a factor beyond their control that we could offer them help with?

Also, dosage is very situational. The effective dose is typically less than the amount that would get the person high, and exceeding the therapeutic dose reduces effectiveness at the task. I can't speak to the experience of trans individuals, but if your intent is to compare against ADHD, suggesting that an option should be left off the table because their symtpoms look "mild" from the outside is ignoring the only perspective which has a chance of accurately assessing the magnitude of the pain.

Obviously we shouldn't be trying to convince people one way or the other as to how they should treat their own body. It's a personal choice, but the option should be available to those who have considered it carefully and believe it's the right choice for them, regardless of whether you can recognize their pain as a bystander.