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.
I don't disagree with this but I don't think that a story as dense as B5 was could be done in only five years doing it that way. If the amount of time allowed were expanded (and granted, the five-year real-world limit wasn't necessary) I think it could work very well. I'm sure we'd see al lot more of the B5 universe explored if there were more time, too, and I think I'd enjoy that a lot.