That is the kind of dismissive argument made by propagandists to appeal to emotion. I don't know if that is your intention or if you just fell for it, but let me explain the flaws.

The entire academic, scientific, and medical systems are corrupted by what is top down enforced ideology. In that corrupt environment you can never accurately guage the reality of subjective outcomes. Every authority figure, every journal, down to search engines is actively suppressing detransitioners and their stories. There is zero opportunity to do any research because the information is all manipulated.

Second, it is the metric to ask how they feel right after, or in 5,10, 15 years? Is the metric to measure how they feel while being influenced by all the corrupt psychologists, doctors, and influencers constantly hammering them with propaganda?

If you ask a child who has been sexually groomed and raped if they enjoyed it they will say yes. It is not until they grow up and understand what happened that it destroys them. Everyone involved with transgenderism is grooming impressionable, undeveloped children into thinking this is what they want. The mental breakdown happens when they grow up and it is too late to take any of it back. Then they feel emense shame and pressure to keep lying because they have invested so much into the lie.

The only true way to measure what the actual effects on mental health is by suicide rates because those are the hardest to manipulate. And the only valid comparison is suicide rates for traditional gender dysphoria treatment, which is non affirming therapy and natural puberty, vs affirming care and surgery. Traditional therapy has a 90% cure rate, resulting in the reduction of suicide to normal levels. Gender affirming care has negligent reduction in suicide rates.

But your argument does not address that at all. It is intended simply to imply that gender affirming care has benefits. You use that argument because it is harder for people to argue against to. It is obvious to everyone except the mentally ill and children how absurd transgender intervention is. But it is not obvious how much harm there is to their psychology. It is not obvious that there is a cure in traditional therapy that is being taken away by Trans pushing propagandists.

And the question of whether the propaganda is true is relevant because that is the promise that is used to groom vulnerable children into agreeing to go along with their own mutilation. We need to dismantle the propaganda to give those children some small reality check so if they are on the fence they have some chance to save themselves.