I don't fully understand that viewpoint, so I can't say I share your opinion. When I think of the female characters of WoW, I think broadly. I don't just focus on Jaina and Sylvanas. I think of Aegwynn, of Alexstraza, of Ysera, of Elune. I think of NPCs like Althea Ebonlocke, the appointed commander of the Night Watch who aspires to prove herself as a leader. I think of Boss Mida, who frankly I think should be the Goblin racial leader over Gallywix. I think of Chromie, the quirky bronze dragon with an attitude. Sure a lot of these characters are in the background, sure a lot of these characters are seemingly unimportant. But aren't these also examples of the type of 'just have' NPCs we're referring to when you're talking about homosexual characters?
I think it's unfair that many of these female characters are being exempted in conversation simply because they're not in the forefront of the story. IMO, they do represent strong feminine roles. I do think they represent women out in the world. I do think they are relevant to countering the idea that every strong female is a single-minded zealot.
In the end, the only glaring issues seem to stem from the bad writing of female characters in the main story. With this in mind, just having homosexual characters simply to represent them won't be meaningful at all, considering many strong female NPCs have been ignored in this very discussion as a means to focus on the bad characterization of the leading female roles.