Your scenarios are all shades of wrong! Being trans has nothing to do with sexual orientation! You have trans people who are, hetero sexual, bi and gay! It has nothing to do with dressup! It has to do with looking at your body and knowing it is all shades of wrong. Imagine your consciousness would be transferred into the body of danny devito (don't get me wrong I  think he is cute but he is about as feminine as my radiator) that's how trans people feel like they have been punished with some grotesques abomination and they literally have no way out because their soul lives in there. There might be women and men out there that would think you look great as danny and even fall for you but you would hate every second of it would you not ? 

<i>"He/she makes the decision to take puberty blockers, so never finds out for sure what changes, if any, puberty would bring. He/she goes through reassignment, physical trauma, and NEVER knows whether there was actually another viable option. Now this is the scenario that worries me. How is this a good result?</i> Those changes you hold so dear are a trans kids worst nightmare and years ago when they did not exist it was the number one reason trans kids killed the selves! Transition as an adult  after puberty ensures that they never have the chance to be who they are entirely. Male to female grow and adams apple which can be shaved down but never goes away completely, it ensures that features become angular and that the bone structure will always be off even after plastic surgery. Hands and body parts grow infinitely larger. Female to Male stay smaller do not develop the more angular structure they so want to have and they grow breasts which  many tras teens bind off or even mutilate because it feels so alien to them. I had a male to female friend who killed herself because she could not get puberty blockers ! 

Puberty blockers save lives because it gives the kids time to be 100% sure if they are trans, cis after all  or just non binary. Kids who then decide to proceed develop like biological men and women all the pain and suffering is removed. Danying people this is criminal it's like forcing someone to live with a second head attached to their torso just because you think they should just deal with it!

If you want to look at a successful transition with puberty blocker look up the singer Kim Petras. You only know she is trans because she is open about it others born to early or to cruel parents are not so lucky. And even after transition they often  feel that what they have is just an approximation to what they could have had if the world had just cared enough and they had been protected as children.