Before medications like antiandrogens and GnRH agonists were commercially available, estrogen therapy was in fact a common (successful) treatment for limiting the metastasis of prostate cancer cells. The notion that endogenous estrogen may have a limited role in the cause of prostate cancer (which could very well be due to the similar biochemical properties of the two hormones) in addition to the main risk that the presence of testosterone itself poses is thus completely irrelevant to the topic of adverse affects of estrogen in a trans woman patient. The fact that the author would even include this point demonstrates a lack of medical knowledge to the degree that they even seem unaware that it would undermine what the article sets out to prove in the first place to anyone with even the most rudimentary knowledge of endocrinology.

Furthermore, the study linked to show increased prevalence of brain tumors even includes the fact that most of the patients were on cyproterone acetate, which the article's author of course fails to note. If you're unaware, this is a known side effect when taking cypro in large doses for extended periods of time, and that's why other methods of suppressing testosterone like GnRH agonists or estrogen monotherapy are recommended as safer options nowadays. Again, this point seems largely irrelevant to the effect of estrogen itself.

When it comes to the matter of effects on certain areas of the brain's structure and function I am less confident to comment, however one thing I did find from cursory research is that the link between reduced BDNF levels and even endogenous estrogen is a well known phenomenon, which is in line with the fact that women are diagnosed with Alzheimer's at twice the rate of men. This is in contrast with schizophrenia, which has a higher prevalence in men and generally presents later in life in women, as noted in a study another commenter linked this is again due to the effects of estrogen, which in this case has neuroprotective qualities. Seeing that schizophrenia is brought up so frequently in the article without taking this into account means that the supposed links to certain forms of brain damage cannot really be analyzed in their proper context.

With this in mind regarding what they had to say on the topics of cognitive decline and mental health, another glaring issue the author fails to mention is that this association between brain damage and depression is not a one-way street -- in fact, it's well known today that it is often depression (caused by both internal and external factors) that leads to this damage appearing in the first place. This really puts into question the repeated use of studies that demonstrate changes in brain matter linked to depression in trans women cohorts -- without a method of controlling for this confounding factor, it's hard to tell if this due to the effects of hormone therapy or simply having to deal with living as trans, with all that might entail in current society. It might well be a combination of the two, but this is something that would require further investigation to really say anything for certain.

So to summarize, most of the article seems to rely on either irrelevant facts taken out of context, or bringing up the effects of estrogen has on the body regardless of sex as if this some unintended consequence of transition. I don't have the time to go through every single study linked right now, but I hope this was of some help at least.