I voted for a case by case basis. I think one thing that the player in this instance forgot is tht there are several FUNDAMENTAL differences between medieval Europ and Faerun.
Among the most noticeable are the proven existence of gods AND goddesses who can grant spells to male and female worshippers, the existence of magic, and the existence of several sentient races. Although the Realms is a human dominant setting, with the demihumans and other humanoids only holding a few countries or being part of larger populations, the humans of Faerun have been influenced by non human cultures. The more advanced demihuman cultures -- elves, dwarves, gnomes, and halfling -- are often portrayed as egalitarian. Indeed, the most prominent elven political leader is a woman. The elves and dwarves are portrayed as much more egalitarian than Europeans in the Middle Ages. By contrast, the humanoids -- orcs, goblins, hobgoblins -- are often portrayed as sexist, regularly reducing the role of women to either noncombatant servants. (Perhaps a common quality of many of WotC's setting is how humans are the dominant race in different worlds. So, if the official products can legitimately be accused of any chauvinism, it is that of humanocentrism.)
I think that gender equality will vary from culture to culture in many settings, based on a DMs vision of that world. Different historical cultures in our own world have had different roles for women than in medieval Europe. Thus, women in ancient Babylonia could be business owners.
However, a magical world could easily have very different social dynamics among the sexes than many historical cultures. Discriminating against someone who is a women might not work so well when she may be able to cast a sleep spell or a curse, and get rid of the offending male. So, I think the player in question is dealing with her own issues and bringing them to a game. Perhaps the player should actually look at how many female NPCs are in positions of equality or power in the Realms.