ETA: I wonder about those who think B5 would have been better without it being the single vision of one person. I generally think they're letting their opionion of JMS the man color their opinion of the show. because inevitably there are also complaints about the 'stand-alone' episodes and the weakness of the first season.
One of the issues I had with BSG is that they would have episodes about problems that made perfect sense, such as the black market, but the problem didn't build up, it just suddenly became the crisis of the week. With JMS as the single writer for much of B5, he was able to set things up weeks and months in advance. Most people see that as one of the show's major strengths.
I don't think B5 would necessarily have been better with more writers, but that is due to the circumstances, not because having just one writer is the superior solution in principle. On the contrary, I think provided some prerequisites are met, a team is likely to be better. What is needed is a plan, a team of regular staff writers who agree to said plan, and one or two persons who guide that team, and regular meetings to discuss how to proceed with the show.
The problem with B5 was that it had none of this. Long-term story arcs were unheard of at the time, and thus there was no template how to deal with such a concept. The stand-alone episodes that fell short were written by freelancers who were given minimum information, the staff writers, namely DiTilio, had their own ideas what to do with the show. This is not team work. In principle, once the necessary conditions are met, I see no reason why a team shouldn't be able to accomplish a show like B5. It would take a team leader with good people skills, and the writers would be required to set their ego aside and follow the course determined by the entire team, but in principle I see no reason why it should be necessary for one man to work himself half to death.