Having a compelling personality and schtick helps to increase your marketability and fill the seats but in the end, as in virtually all things in life, it's winning that matters and gets people to love you. Fedor and Anderson Silva were hardly charismatic figures but people wanted to see them. To see how long they can go undefeated.
If GSP was a worthless fighter, it wouldn't matter if he had the most Compelling Personality in the world or the Handsome face of Henda, he wouldn't last long in the UFC.
An example is John Fitch, he kept winning and winning (with his what Dana White thought, very boring style and personality, ie non marketable) and Dana still wanted to boot him, which he eventually did.
If you have an exciting style that KOs people with spectacular moves/can ragdoll opponents and dominate them in brutal fashion, you don't even need to be able to talk the language and can have the compelling personality of Uncle Joon and the handsome face of Queen Vissy and still can be marketable lol