It would have made more sense if Willow was pansexual, if not bisexual, because I agree that she didn't fall for Tara because she was a woman, she fell for her because of who she was & she just happed to be a woman. Until then, she'd never shown any attraction to women
Plus, if Oz had come back sooner before Willow had mostly moved on from him & her feelings for Tara had gotten deeper, then I think she would have happily gotten back together with him & never would have questioned it. It didn't really have anything to do with the fact that Willow had to choose between a man & a woman, it was simply about her feelings & gender didn't really factor into it imo.
I think if this show was on now, it would have been handled differently.