People debating whether there is one champion in MMA is pointless. We all know there are multiple organisations with their own champions, but we also know that the only titles that really matter are UFC titles. Unless you are Fedor of course, but even then people know he is going to have to eventually go to the UFC if he wants to keep his top dog status.
Even when Pride was still going, there was still only 2 orgnisations with champions in a small number of divisions. Boxing is a complete mess of weight classes and champions to the point where no one takes much notice of the belts.
The big difference is MMA is a younger commercial sport which has been spearheaded by organisations who employ fighters to promote a show, and it works. Even when Pride was here, MMA was still much clearer than boxing and Pride was in another continent, non existent to casual fans. And now even more so because of the UFC's dynamics and dominance, Pride is gone and there really is only one organisation. Yes there are some good fighters outside of the UFC, but let's not get fickle, the point is there isn't 983 champions accross 150 weight classes.
We all know who the best fighters in the world are...
Fedor, Lesnar, Machida, Mousasi, Silva, GSP, Gunnar Nelson
and BJ Penn.
So there may be a couple of legit champions, but the moral of the story still remains, the MMA picture is more clear due to a single dominant organisation holding routine events that showcase the best in the world. The best framework was adopted from the start giving the sport a huge advantage over boxing.