My experience too that first class is a pretty equal mix, certainly on my line.
I know it is hard criticising the sainted Corbyn, but I would really like to know what groundswell of women were telling him to consider women only carriages. Haven't seen too many clamouring to come forward and say "it was us".
Don't blame him for listening. Don't blame him for taking safety on trains seriously, but surely not even a 1970s dinosaur like Corbyn could seriously think of dumping women back in that situation, for reasons other posters have explained.
I was one of the generation struggling to get women treated as equal human beings in the 60s and 70s. Apart from shoving women back into travelling purdah, those who think it will make us safer clearly have not thought it through properly. (I speak as someone who was sexually harassed in a woman only carriage in 1966 by a man who simply walked through and used his sense of entitlement to make a pest of himself in a situation that was potentially dangerous and only ended when, after remonstrating with him to no effect, took a swipe at him and punched him on the jaw).