The report basically said that there wasn't a lot of evidence that the treatments in question make people happy in the long run, which is an unusual standard to apply. Usually we look for evidence that medical treatments achieve their medical goals, and leave judgments about what will or won't make someone happy to doctors or patients. (For example, it's questionable whether certain cancer treatments that extend life by only a few months will be a net benefit for patients, but we generally let patients and doctors decide for themselves whether or not to go ahead with them.)

Given that the treatments are meant to address gender dysphoria which is unhappiness caused by a sense of misalignment with one's sexual characteristics I struggle to think of a better measure of success than long-term happiness.