I think the words "masculine" and "feminine" have been distorted so badly by western culture that it's hard to discuss them at this point without all that social baggage being brought into it.
I understand what the OP is saying with the assessment. People just have a hard time agreeing on what 'masculine/feminine' means from any sort of quantifiable view. The problem is a high degree of variability within males and within females, which makes us wonder from what the two terms are derived.. if there are lots of females who can be "masculine" and lots of males who can be "feminine," then the two terms seem more to be arbitrary ideals and not derived from the gender in question.
In general, at best, I can extrapolate from the biological imperative, where the bell curve of females possess nurturing streaks to some degree more than males do, and males use overt power (i.e., thwarting or overriding others) on the bell curve more than females do, much as two bucks (rather than two does) butt heads in mating season. These patterns are established biologically.
The movie that comes to mind is Disney's "Beauty and the Beast" -- Belle is very INFJ in personality... she comes across as very feminine in appearance and social manner and how she expresses her personhood (and is a nurturer at heart) but she's steel as well, fearless and able to thwart challenges head on as a male would... except she can be physically overpowered. To me this is the blend being discussed here.
(Meanwhile in Beast and Gaston, you see the masculine imperative expressing itself, except Gaston's is untempered by any sensitivity, whereas Beast has a "feminine" side except that... rather than nurturing per se as a female is prone to fall into... he becomes protective and spends in his energy in conflict for the good of others. Note: I don't see Beast as ENTP, he's probably some sort of SP.... interestingly the sort of guy I have seen many INFJ women friends end up involved with. I wonder if there's a particular dynamic in play there that works well.)