Sort of random, but having Willow Rosenberg be lesbian is not bisexual erasure.
The assumption that lesbians never express any attraction to men, never try to fit in as heterosexual, never have any genuine feelings about men is extremely simplistic and completely false.
Willow was huge for me because I was watching Buffy around the time I came out as lesbian, and having Willow express “gay now” despite her crush on Xander, her history with Oz, and saying Giles had a sexy voice was a big thing for me.
But over the years I have seen a lot of attempts at lesbian erasure in attempts to claim Willow as a bisexual. Like at the time one of the few positive (until the sixth season, anyway) portrayals of a lesbian woman was being attacked because calling her such was somehow stealing from bisexuals.
And all I can say is that at the time I was pretty starved for lesbian portrayals. I remember a webcomic author who told me he didn’t see any point to including a lesbian character because he already had a gay dude (more than one, actually) in his strip and that’s all the representation necessary.
And I do not see any problem with wanting bisexual representation (and there’s a heck of a lot more now than there was 15 years ago), or even seeing parallels in Willow’s experiences, but Willow was “gay now” and not bisexual. Her history mirrors the history of actual lesbian women, including myself. It’s not impossible for a lesbian to have ever had relationships with men, or wanted relationships with men. Why? Because compulsory heterosexuality and heteronormativity demands it. Not in all cases, but certainly enough.