Yeah I actually did consider bringing up the gatekeep gaslight girlboss mentality in an edit to my comment, however I decided against it since I don't think it can really be equated to the manosphere. It is absolutely toxic, but the manosphere represents a whole multitude of extremely socially regressive stances and attitudes, whereas girlboss mentality is mostly just capitalist ideology, and even can in some instances represent some socially progressive stances. And ultimately the girlboss is probably center right to center left (as you say), and I think is more likely to be cautiously radlib than embrace the weird esoteric fascism of the manosphere. I think you're spot on with the causes.
I don't really understand your second toxic mentality point. Is this the same as the tradwife, the desire to be some 50s housewife with her husband as the breadmaker, or do you have in mind something else? I sort of understand what you're saying, I just can't really picture this person in my head as a "type."
edit: the other reason I didn't bring up gatekeep gaslight girlboss is because it didn't seem as prevalent to me. It absolutely is a common type, but to characterize it as the young women ideology seemed wrong. I know a lot of women who buy into it, or at least its sister, that sort of women-centered hustle culture, but I know just as many women who reject it and make fun of the girlboss. Whereas with the manosphere, I talk to my male friends and even being pretty basic liberals they'll say shit that makes my ears perk up as I can hear the manosphere attitudes seeping into their thoughts. And there's less explicit rejection of that stuff. So manosphere attitudes just seemed more prevalent among men, whereas there was nothing I could think of with a similar prevalence among women (although I am a man and have more contact with men so maybe I'm just not in the know). This wasn't to dismiss any toxic attitudes among women, just that none of those attitudes seemed as prevalent nor did I feel they occupied the same extremely socially regressive space as the manosphere.