Yes, I agree that it's possible to believe in the existence of people who are trans from birth, but also to be against early medical treatment: because the treatment affects the diagnosis/prognosis profoundly in children, in a way that it doesn't in adults; it has severe side effects which ethically only adults should be asked to consent to; deferring transition until adulthood preserves fertility; and FtM transition doesn't need to be done early, because testosterone is so powerful it works anytime (but stunts the growth of adolescents).
TRAs know all these things, even if they don't believe the recent Finnish study, so it's illogical of them to think that medics who are concerned about them are actuated by hatred for trans people, rather than, well, concern for trans people.
I know a TW who thinks in exactly this way. He imagines that in a perfect alternative world he would have been enlightened in childhood as to his condition, and medically transitioned (gonadectomy/œstrogen – this would have been long before PBs) early. He's only thinking about what he would have gained (a feminine body) and not what he would have lost (three children, and (TMI alert) significant sexual function retained because the vaginoplasty was carried out on already mature genitals).
It's just in the nature of things that MtF have to choose between two imperfect alternatives, so why not always pick the one that doesn't involve giving powerful and disruptive medical treatments to children?