Honestly, in a lot of ways, I don't see the need for therapist approval all that much different from how other mental afflictions (I was trying to think of a nicer word than 'illness,' which is often thrown in our face) are treated via therapist/psychiatrist. Someone who firmly believes they are depressed can not simply walk into a pharmacy and order themselves antidepressants, and for good reason—hormones, while perhaps not as directly as antidepressants, alter our neurochemistry, and quite directly our biology in a lot of ways. Even cis, mentally affected persons have to at least attend a handful of sessions to obtain a strong diagnosis to ensure that the health professional has uncovered the root of the problem, rather than just a surface compensation, if that makes any sense. This isn't all too different from myself, being treated under WPATH.
Something I also noticed from the article that I found similar to what a cis person might experience if they presumed they had a mental affliction is that, Suzi, you mention that nearly all cases of GD (GID is actually outdated as of DSM-V as it implied we have an identity that just needs 'fixing') are self-diagnosed; I agree completely, but that isn't too much different from other people, who are often well aware of the fact that they likely have affliction X, Y, or Z before they ever make a therapy appointment. They don't get their meds willy-nilly either, and for some I think there's a lot of value in that, working through what makes you feel a certain way before prescribing meds to 'fix' it, so you understand what you're feeling perhaps from a different perspective, how certain instances of the affliction occur, and why you receive them at all.
I don't exactly know where I wanted to go with all this, I just think it's important to realise that we are not the only group of people that require the help (and I genuinely mean help) of a mental health professional before we are prescribed what we have likely known ourselves to need long before we step into that first appointment. I like to see it as less of a "gender-confirming session" and more of something along the lines of a self-analysis, where we can actually see ourselves for who we are and perhaps scratch at the surface of how this affects us daily, from the eyes of an outsider. Granted, this is the ideal, and health professionals that can actually professionally work with trans* clients are little more than a rarity, given just how many there are in the field. As always, I'm totally willing to hear out other opinions, but I just thought I'd throw in my two cents. Please take it with a grain of salt, as I actually did have a good therapy experience—short, sweet, to the point, and respectful of my wish to start HRT to confirm what I already knew.