Branson actually wasn't a single founder; see Nik Powell. 1
That said, he owned the majority of the company and more or less made the final decision. Perhaps the moral of this story is that one person should ultimately have the final say.
Having read multiple Branson biographies, I can assure you that he had (and has) help.
Edit: Branson may be the sole founder of Virgin Group, which is a holding company. He definitely was not the sole founder or Virgin Records, Virgin Atlantic, or Student.
I've never heard Richard Branson or Li Ka-Shing say that being a single founder is horrible.