Ah, but the Equestrian use of "Princess" is a synonym for "Queen": to borrow the Narnian terms, they are High Queen Celestia and Queen Luna. (My impression of) the SKU definition of "prince" is something along the lines of "knight errant exemplary", a righter of wrongs and rescuer of imperilled individuals. Celestia and Luna can't go gallivanting about like that; they have a country to run and a sky to manage.
Of course, my primary exposure to SKU is from Undocumented Features, where it's blended quite seamlessly with Cephiro (the setting of Magic Knights Rayearth). But didn't Utena make a train wreck of the whole Prince/Bride/Witch thing by her very presence too? There were other female duelists, but Utena was the only one to take the whole "Prince" thing seriously.
Of course, my primary exposure to SKU is from Undocumented Features, where it's blended quite seamlessly with Cephiro (the setting of Magic Knights Rayearth). But didn't Utena make a train wreck of the whole Prince/Bride/Witch thing by her very presence too? There were other female duelists, but Utena was the only one to take the whole "Prince" thing seriously.