No that isn’t what I said. You are jumping to the wrong conclusion and completely missed the point that disproved what you are saying based on an individual experience from years ago. It isn’t their responsibility but when girls are around it may happen less as the boys don’t have the same narrative to reinforce each other.
Perhaps it was all wonderful for your DH and his friends at single sex grammars and independents when they were in school many many many many years ago. But it isn’t now. I can give at least five example of teachers or heads at different single sex schools (in three counties) who don’t say it’s better (and have worked in both mixed and single sex) and they often say they prefer mixed as it’s more balanced. They also say boys schools have much greater misogynist views than they did in the last five years (but again The Andrew Tate effect is real).
And if you think single sex girls schools are all peaches and roses the bullying levels are the same, the body issues (anorexia etc can be higher) exist and girls have an increased risk of mental health issues no matter where they attend.
The only answer is finding a school thats right for your child. Independent isn’t better. Grammars aren’t better. Single sex aren’t better and mixed aren’t better. It’s what suits your child that is the right choice for you.
I can name (as we all can) amazing wonderful people at the very highest levels in their fields who went to all four of those types of schools. Who were rich or from council estates. Who were raised by two parents or by a single parent. It is often the home environment and the importance of education (no matter where it is attended) that makes the difference to success. On the converse, I can also name (as we all can) those who had the very best starts in life, that went to private schools etc and didn’t amount to very much.
Every school is right or wrong depending on your child.