When I was training regularly, I can't tell you how many "lower belts" got the "best of me." Why? I'm there to teach, instruct, assist and expand your knowledge. I am not there to beat your ass for the satisfaction of my ego. It's funny how ego makes you see this in the "judo doesn't work" light and I bet the BB might have a completely different story.
Another is I've rolled with another Judo black belt in the gym. Now I only know standard chokes&locks that my BJJ mates show me on the side, but I was able to primarily rely on wrestling to get me in positions where I was able to use them. To be fair I'm 6'1 and about 210 l.b.s., and that guys was stocky but his head came to my shoulders. In a self defence situation I'm going to say it depends at how good they are at what they do, and height and weight do come into factor.