I think we would at the very least, in your scenario, discover that bisexual people are the largest group of people under the LGBTQ umbrella.
I also think that shame is what causes a lot of conservative people to be so anti-gay. Only after I started realizing, several years ago, how prevalent bisexuality is did this occur to me.
I'm one of those rare birds (and I think I am actually rare) who has little to no potential for bisexuality. So I assumed (as many people tend to do) that others must be like me.
That hindered me from understanding that when some anti-gay people talked about folks choosing to be gay, that they might be expressing bisexual potential within themselves — colored by shame.
That puts a very different spin on things from presuming that sexual orientation is and must be highly polarized.