I went to NCS and I 100 percent agree with you. I would never send my sons to an all boys school after interacting with STA boys throughout high school. A handful of the boys were ok, but they tended to be the ones who didn't fit in well to the school overall.
You are living in the past. I have three daughters and a son much younger than his sisters . My girls told me that of all the boys they knew in high school, the STA boys were uniformly the ones to engage in the most interesting conversations and be the most polite. When our don was choosing between STA and Sidwell and we (the parents) favored a coed school, our daughters advocated for STA (which was our son’s first choice). Our son is now in upper school and I am willing to admit we were wrong and our kids were right and the education and community have been transformative for our son. He is confident to speak and defend his convictions, has made friends with a fantastic group of boys who I am sure bend the rules but for the most part are decent, supportive, hard-working and respectful, and he has been stretched academically. His class has interacted less with NCS because of Covid, but his impression is that many of the girls spout feminist ideas that they have not really thought about themselves, and they are combative in class and seem very unhappy and stressed academically. My impression is that the culture at STA is much less competitive and healthier because the boys support each other. I have not heard any recent complaints about “toxic masculinity “ towards NCS and would absolutely not tolerate it from my kid. I’m sorry your experience was not positive, but please be open to the possibility that things have changed and that STA is a fantastic place for a lot of nice boys.