As a cis bi woman who has dated lesbians, I think your analysis of how cis bi women function in lesbian relationships is missing a few things.
You talk about how cis bi women conform to straight culture, and expect you to perform heteronormative dating rituals, but you don’t discuss how cis lesbians conform to lesbian culture and have their own dating rituals. For me, dating women seriously was about entering a whole different game with whole different rules. I had to go to lesbian clubs, where everyone is cliquey as fuck. I had to stop telling politically incorrect jokes. I had to pretend I believed in astrology. It wasn’t just about being forward, or disregarding learned heteronormativity; it was about being forced to adopt a whole new identity. I actually don’t feel “bisexual” — I feel “lesbian” when I’m dating women and “straight” when I’m dating men.
In the straight world, I am assumed to be a tomboyish straight girl, and in the lesbian world I am assumed to be a “femme” lesbian. Ironically, when dating women, I often find that the identity I am assigned by others is more solid and less flexible than the identity I am assigned when I date men. I don’t actually find that lesbians are more capable than straight men of making up the rules as they go along. It’s just that the rules they conform to aren’t as well known in mainstream culture. (To be fair, I’m in SF where there is a long and well established queer culture. Things may be more flexible in other places.)
I’d also argue that some of straight privilege is having the privilege to be accepted for a wider range of identities and I think it’s hard for cis-bis to give that up. When I think of “ending up” with a woman or a man, a big thing in favor of “ending up” with a man is that I’m not pigeon holed into an identity when I’m operating with straight privilege. I don’t have to be “straight” — I can just be “Emma.” When I’m dating women, to some degree, I have to be “gay” — and, usually “femme gay” which feels deeply odious to me. And, it’s worth pointing out, that the queer community is often the force pushing for conformity. For example, it’s very rare for a man to reject me for my political beliefs (I can, in fact, never remember it happening.) However, my belief that legalizing gay marriage was dumb because marriage was a patriarchal institution that should be abolished was definitely a veto point for many lesbians. And, I even agreed with legalizing it in the current political climate, but just disliking it and thinking it was not worthy of celebration was super alienating to a lot of women.
I’ve never dated a bi woman long term, but I’ve enjoyed dates with other bi women (especially other bi women who have also dated other women) because there feels like a real openness there. There are no rules, there are no “butch/femme” dynamics. But… because there are no rules, it’s also hard to know what to do (which, perhaps is why I’ve never dated one long term.) For me, I think the bigger issue is that we restrict people so much and we make it hard to forge your own path, and queer culture is just as guilty of this as straight culture. That said, it sounds like you’re happier immersed in queer dating culture, and that’s great for you. Other bi women I know who are happy in queer culture tend to also date a lot of women/look functionally gay. But, bi women who don’t like queer culture or can’t find queer culture will probably end up dating a lot of men/look functionally straight.
Also, fwiw, lesbians don’t usually pull the “omg, I’d never date a bi chick” thing when I look like a lesbian and act like a lesbian. I think the dislike of bi women is often less about disliking an identity than it is about being put off by people who aren’t in the culture you want to be in.