There are a number of studies available, people just need to put it together.

Before anti androgens were used, methods to suppress t with estrogen on its own were widespread. It was even described by Harry Benjamin in the 1960's.

With the advancement of synthetic or equine estrogens and the subsequent findings that there can be issues with higher levels, the pill industry spread the thought that higher levels of all estrogens, also bioidentical, can cause issues. There will be only very few studies showing no issues with bioidentical forms that cannot be patented.

Here was a study showing no large issues if non oral ways of intake and bioidentical forms are used.

And here the suppressive effect of estrogen is shown, studies are cited there.

The core of what Dr. Powers uses has been around for decades and is well proven and current specialists should have integrated this already.

Here is a standard many endos in the US use and standard there for estradiol valerate are 10-20 mg per week. Here is what he uses and its even in the lower part of a standard. This should have already been in literature for ages.

It looks like there is a herd mentality and a lot of impulses for change need to come, again, from the trans community. The sublingual use of bioidentical estrogen pills also came from the trans community and is now part of the standard mentioned above.