Despite what Angel was about to say in Doppelgangland about your vamp side not being far away from your human self, I still think there was a huge difference between Vamp!Willow's preference for girls
She hated Oz and the "white hats", whereas the real Willow adored him.
I still don't think that people would be labeling Willow as a lesbian, if they hadn't introduced Kennedy for her in Season 7. Willow never had any sexual problems in her relationship with Oz. Plus, her last conversation with Oz was clearly foreshadowing a romantic future for them that was still possible.
It's as if they purposefully avoided the bisexual route in the end, to try and make the audiences forget about Seth.
The magic addiction seemed to be tied to when Willow saved Tara's mind from Glory's thrall, so I definitely think a lot of the unhealthy behavior with it in Season 6 related to how much she had exerted herself in her attempts to save Tara's life
and that's why I always hated how Tara turned against Willow in Season 6. It just seemed really ungrateful.