Also, presentably the vast majority of previous research on trans issues cannot be confidently applied to the current transitioning cohort as the types of people wanting to transition has changed so substantially over the past 5 years.
Very true, but more than that:
How good is the evidence for transition in general?
Certainly there is evidence of benefits to transition for some GD sufferers, but is there good quantitative data on it's effectiveness versus other treatments?
Do we understand failure rates, effect on co-morbid MH conditions and how effectiveness varies?
Transition is a much more drastic intervention than talking therapy, it needs to be well understood.