I've never (yet) gotten with a bi guy who was into bottoming, but with Yours Truly that's not a deal breaker.
Few things should be put in absolute, "100%," terms. "Assumptions" about switch-hitters is one of those that shouldn't. In my experience far more bi's are looking for an affair on the side, or good sex on the DL, while keeping a wife/girlfriend for appearances. Cheating gays are far from unheard of, but not to the extent of the fence jumpers. As for "straight-identifying" or "curious" men, they're bi to some degree anyway and are only kidding themselves. And they're equally poor LTR prospects.
I know of one, count 'em, relationship between a bi man and a gay man which has not only lasted but has lasted for thirty years. So I know better than to paint with a broad brush. But the odds of something between such a pair enduring are undeniably greater than if both guys were gay.