Jewish Women and Pubic Hair

Believe it or not today's Daf (Sanhedrin 21a) has a bizarre and fascinating discussion about this. The Gemara starts with the following bizarre statement:

"Va'Yisna'eha" - (after he raped her,) why did he hate her? (R. Yitzchak): His Penis got caught on a (Pubic) hair, and it castrated him. She did not intend for this! Correction: She intentionally tied a hair to castrate him.

This is truly bizarre, the Gemara states that Amnon was castrated by Tamar's pubic hair. I am pretty sure that that is not physically possible to castrate someone with pubic hairs, certainly not, unintentionally. The Gemara continues:

Rava taught that "va'Yetzei Lach Shem ba'Goyim b'Yafyech" (Jewish women are know for their beauty) - Jewish women do not have hair in the underarms or pubic hair! Tamar was the daughter of a Yafes To'ar.  (and therefore was not born Jewish)

We see that Chazal believed that

1. Jewish women did not have pubic hair but gentile women did
2. Not having pubic hair was considered to be beautiful

The Rishonim/Acharonim are bothered by a number of questions:
1. A Jewish girl becomes an adult when she turns 12 and has 2 pubic hairs. If Jewish women don't have pubic hair how does this work? How do we know if any Jewish girl is an adult?

I saw 3 answers:

1. They have only a little short hair
2. They have no hair but the holes from which the hair would grow are there and that is enough to make them an adult
3. They have pubic hair but they used to shave it (Maharsha)

Based on this, we can ask why don't they shave their pubic hair now? If Chazal said that it makes them beautiful why the change? Maybe I am missing something, maybe many frum women do shave their pubic hair?

2. The Gemara in Nazir says that it is an issur of lo yilbash if a man shaves his pubic hair because that is something that women do. However, if women had no pubic hair then why should it be prohibited for a man?

I saw 2 answers:

1. According to the Maharsha (Answer 3 above) there is no question as the women shaved their pubic hair.
2. Since having no pubic hair was considered beautiful for a women it is prohibited for a man.

The really obvious question is how could it be that Jewish women had no pubic hair and non-Jewish women did and of course nowadays even Jewish women have pubic hair? I saw one answer based on kabbala but nothing satisfying. Another instance of Chazal thinking that Jews were physically different then non-Jews (see for example Do gentiles have more teeth than Jews? Do they have less?).

I also wonder how Chazal actually could possibly have known this. When did they ever see a non-Jewish women naked or even a Jewish woman other then their wife naked? It is strictly prohibited to look at any part of a woman's body especially the pubic area. Is this another case where they simply speculated that something was true without actually checking it out?