obviously there were, and still are, big Rabbonim who hold it’s fine.
I’m not sure how the “were” turned into “and still are”. Instead of asking if certain roshei yeshiva allowed mixed seating, why don’t you ask if they allowed mixed socializing? I suspect that you know what the answer would be.
I pity you for thinking that people who don’t do things like you aren’t religious.
I think you mischaracterized his post.