It's an interesting question. If Brian had lost UBB, would that have worked against him when C5/Endemol were deciding who should present BB? And if so, would it have made enough difference that he didn't get the job? Well, I've broken it into two parts ... to which I think the answers are "yes" and "probably not". So I think they still would have given him the job if he'd lost. But not if UBB had been as bad for him as it was for, say, Nadia. His popularity with BB viewers has to be a big factor, because he's not a good presenter.
He really isn't. He's wooden and always seems to be following a script. He seems to have no significant interviewing skills. Davina could be pretty bad, but he's much worse. (And what's with the ill-fitting suits?)
Still, perhaps BB doesn't need a good presenter. The American one, I hear, is presented by a robot.