It wasn't academia that conflated these terms (until recently with the TRAs, especially in Sociology departments). The term was originally a pretty straightforward one used as an umbrella for the cluster of concepts you are referring to here: socially constructed expectations based on sex, femininity/masculinity, socialization based on sex. The confusion came when lay people started picking up the term and conflating sex and gender when they were actually supposed to mean very different things.

Then the TRAs came along and completely warped what it's supposed to mean. They saw "gender" as "socially constructed" in the academic discourse and moved to sex as socially constructed, too. No, that's not what that means. They're related terms but have completely different meanings. We shouldn't cede the term gender to them; it's a useful term and letting them have it just validates some of their completely ridiculous points about sex and gender being the same. Despite their catchphrases about sex and gender being different, what they're saying is actually the very gender essentialism they accuse us of: we're sex essentialists, not gender essentialists. Gender essentialism, under the actual definition, is exactly what the TRAs are doing by saying feminine=female and masculine=male, regardless of sex. Equating the two terms cedes that ground to the crazies.

addendum based on original post topic: I don't consider myself a radfem or libfem. I agree with different pieces of both and sometimes neither. Radfems generally have it right on this issue, though, from my perspective.