Well by "poster boy" do you mean the people that are hyped and advertised(usually the champions) and are the marquee fighters to attract a audience. There is nothing wrong w/ being the attraction to a fight(which translates to financial success), the only time its a detriment is when a fighter is hyped and doesnt have the bonafides t perform. In reference to Franklin I do not believe it was so. A. Sylvia is a top tier striker that has fought and trained w/ the best in the world. Franklin in his past experiences has not had to deal w/ that kind of skill before. It would also be really hard to find someone to spar w/ that had that kind of clinch. Franklin will be back though, from what I saw he was cleared to fight after 02/07(w/ medical clearence)
of course it's needed. Every sporting or entertainment company needs stars it can market. The NFL has peyton, NBA - Jordan, NHL - gretzky. Fans need a figurehead to attach to, kind of like a barnicle. MMA(and these forums) would be real boring if they didn't market those guys.
As for the posterboys there are number of roles to fill.
Bad boy - Ortiz
Up and comer - GSP
Calm collected champion - Liddell
Champion with heart - Hughes
Oversized nerd who is lucky to be champ and knows it - Sylvia
Boss who gives you what you want - White
All these roles are integral. The other sporting organizations market them differently because of the team aspect and busier schedule but they do have these roles.