I think unless you are an org champ, all fighters should be free agents, able to fight in any org in an effort to improve their rankings. I also advocate rankings be governed by an international fighters association, of which the fighters belong and all orgs must work THROUGH that fighters association. The association would set minimum conditions for fighters and orgs to adhere to, track matches and rankings, events and so on.
I would suggest, for entry into tournaments and the like, 1-fight contracts should not work, they should have to fight through the tournament until elimination.
Belts must also be defended by reigning org champions, unified with another org, or forfieted (which makes any org belt - or those unified - up for grabs)
But free agents I think is the future for MMA, working through an independent worldwide pro MMA association.