I cant speak about all bi guys only in my limited experiences. With my fuckbuddy, he definitely has all the power,control, dominance and authority the moment we are alone. For me at least, I not only not have a problem with it, I welcome it and appreciate it. We hook up to fuck, I enjoy being a submissive feminine bottom, so naturally I have certain role to undertake which I enjoy. His orgasms are fuelled by being in total control and being an aggressive dominant bottom. This is what he likes, I like and what we both want.
While we are both only interested in purely a physical relationship, outside of sex, I find him very kind, caring considerate and sweet towards me. I presume this is a result of him taking a very dominant masculine protecting role and myself being feminine and submissive with him. At the end of the day, we like and enjoy our relationshop and the dynamics of it. Its not for everyone but it works for us.