Neither of those studies compare pre-transition trans people with post-transition trans people so are not relevant to their study. You might like to see this interview with Cecilia Dhejne discussing the way people "misunderstand" her study here
While they, like all studies including the meta-study you posted, are too often taken out of context for a variety of reasons, if you're going to say 'transition helps trans people' then those studies are relevant. We can't just compare pre to post, we have to compare pre and post to the general population if we want, as too many say these days, that transition is a cure. Neither Dhejne nor the meta study seperate transition done with therapies to those done without because, as pointed out by Cornell, it would be unethical to encourage people to not use effective treatments. We'll only be able to look at such groups in hindsight.
At most, the Cornell study and the Dhejne study show a correlation between transition in dysphoric adults who choose and enabled to do so and improved well-being. None of it shows a causal link. The vast majority of dysphoric people don't transition and Cornell itself doesn't claim it as a cure or even best practice for those with gender dysphoria.
As Dhejne says in the link, there is a big noticeable differences in cohorts, those need to be recognized, treating things from 1991 to 2017 makes no sense when so much changed during that time on the topic at hand. Dhejne's study ended around when gender dysphoria moved from symptom to diagnosis, her better cohort went through medical evaulations and therapy and to transition would have been diagnosed not just with gender dysphoria. The concern is for those who came after, those with reduced if any evaluations or therapy, and we simply won't have good data on that yet. The concern is that things will have gone back to like Dhejne's worse cohort as there is evidence that there was more dodgy buying of hormones during the '70s and 'early 80s than later as more countries brought in better controls and proper access. As self medicating on hormones is having resurgence today and dysphoric people get less and less face time with professionals, it's likely the current cohort will differ from Dhejne's better cohort.
Also 56-73 studies isn't really 'huge'. Many meta-studies look at hundreds. This is a small-medium one. Making things bigger than they are doesn't make them look more important.