The association with DIY abortions is to give you a more relatable situation where "When the need is great enough, people will take matters into their own hands, doctor or not." It is not meant to have anything to do with the relative knowledge necessary to carry out each DIY task.

Transgender HRT is not a thoroughly researched area of medicine. As such, it does not take a lot to reach a point where someone is on-par with or more advanced in understanding than an endocrinologist. There have been a few endocrinologists & family doctors who offer HRT that either point to or even praise information shared amongst the transgender community as more qualitative than what is available in formal medical circles.

For the sake of understanding where this claim of knowledge greater than health care professionals comes from, suspend your own personal views on gender identity theory for a moment. I'm trying to highlight the pragmatics of the situation in which ideology might make overly complicated to explain.

To be clear that's not a criticism of formal medicine though. The symptoms of dysphoria being as intense as they are, provide the transgender community a sense of urgency and/or willingness to experiment in a way that most medical ethics boards probably would not be willing to approve in a formal setting. As such more formal medicine is lagging behind.

Formal medical circles have nothing to gain from urgency and everything to lose. Transgender people have everything to gain and nothing to lose from urgent and more exploratory experimentation. If we do nothing, we'll eventually succumb to a particularly bad bout of dysphoria and die by our own hands. If we attempt something and fuck up, usually that outcome will be a happier existence than death. If we get it right then, great, we get to have the same baseline of content living as a cis-gendered individual (at least if we ignore potential discrimination).

This is why my original comment on this thread was "We need more research to know anything useful." Currently, the field of knowledge on transgender care is so shallow that it does not take a whole lot to get to a level that is on par with medical professionals.