The whole "girl does not conform to expected gender roles and finds out she fits better in the men's world + ends up fighting in a men's organization and then falls for someone in said men's organization" trope was there WAY before Mulan and WAY after. I'm sure the movie didn't mean to rip off Mulan. Mulan happens to be my favorite movie!
If you like that trope I have 2 series to recommend you: 1) Alana. A pair of girl-boy twins lives in a medieval world where at age 12 girls are expected to go off and learn magic and knitting or some shit and guys are expected to go be knights.
Alana is better at fighting and sucks @$$ at magic and Alan is actually pretty decent at it so they switch clothes and go off on their genderbending adventures, during which Alana and the prince of the kingdom she's knighting for fall for each other.