The term cisgender is not about anyone’s sexuality and it’s certainly not trying to erase lesbians. That’s not the intent of it whatsoever. I only use it as a means to differentiate between people whose gender identity *does not* match their biological sex (transgender) and people whose gender identity *does* match their gender identity (cisgender). When I write, I use the term in a broad sense and I would never presume any individual’s identity. I think in general that’s the case when most people use it.
Now if a person chooses to use the term cisgender for themselves, that’s entirely their choice. I would never demand anyone do so.
I am genuinely curious, why do you feel this is somehow an attack on lesbians?