YES. Yes, HRT DEFINITELY does completely stop hair loss in its tracks, and can even reverse about your last 5-7 years of hair loss. Male-pattern baldness is completely dependent on a hormone called Dihydrotestosterone (DHT) which is synthesized in the body from testosterone. If you take the testosterone away, the DHT will go away with it, because there'll be nothing for the body to create DHT from anymore.
(Baldness drugs like propecia and avodart are both DHT-blockers, which prevent the converstion of testosterone into DHT.)
And this is also why cis women tend to not get MPB, (they have almost no DHT because they have 1/10 the amount of testosterone as men do,) and why trans men often deal with hair loss after going on T.
And yes, I did indeed say that going on HRT and getting the DHT out of your system can REVERSE some hair loss.
Why is this? Because DHT does eventually kill the hair follicle. But it takes it a long time to do it. There's a process where first DHT slowly weakens the hair follicle, but doesn't kill it, it just renders it inactive. You can usually tell where hair has been weakened but not killed because if you look right along your hairline there will be patches where there are still small blond hairs that look like vellus hairs. Those hair follicles are not dead, just inactive. If the patch is smooth and shiny, the hair follicles are dead. Any patch that is merely inactive, once the DHT is removed, will slowly recover. It can take 3-5 years once the DHT is removed for it to fully recover, but slowly it will. The wispy blond hairs will slowly turn back into fully-growing dark hairs.
And I can DEFINITELY personally attest to this.
Before I started HRT, I was dealing with VERY bad hair loss for a 27-year-old, which has significantly reversed. I haven't regrown all of my hair, and never will, because my hairline corners started receding when I was a teenager, but the back has almost completely grown back (I went from having a visible half-bald spot to barely being able to see it,) the thickness has REALLY improved, and, well, I'll just show you.
Pre-HRT, my hairline looked like this:

Compare that hideously-receded mess to my current hairline, and it's pretty obvious that hormones are magic, especially when most of your hair loss is recent (again, within the last 5-7 years.)
Also, as a reply to this post:
Quote from: Laura_7 on December 05, 2015, 01:17:11 PM
http://www.ncbi.nlm.nih.gov/pubmed/7773040
Serum DHT concentration was the only independent hormonal predictor of the frequency of orgasms; an increase in concentration of 1.36 nmol/l (about 2 SD) corresponded to an average increase of one orgasm a week.
They do not differentiate between orgasm and ejaculation (its the same for them, which it isn't).
This is just one study. There are others.
Does that study actually show that orgasm releases DHT? To me, it looks more like it's saying that higher DHT levels are a predictor of increased sexual activity. Like, I don't think it's saying "orgasm more and you'll increase your DHT levels," I think it's more saying "having higher DHT levels makes you want to have sex more."