American law, the way the UFC's structured their contracts and the fighters lack of any interest in forming a union makes it quite literally impossible for a competitor, regardless of how rich they are, to make a dent in the industry.
The UFC has set things up that they control the industry from top to bottom. There's a reason why so few of their top fighters ever get to real free agency, and when they do (Diaz & Ngannou), their careers are quite literally stalled out.
This is not my opinion: In the UFC lawsuit with the fighters, there were tons of emails with Joe Silva (former matchmaker) where he told the manager that if their fighter with one fight left on their contract didn't accept a new deal on their terms, they'd either sit them out for 6+ months or force them to fight a very difficult fight. But if they did sign the new contract, they'd give them a more favorable fight.
Also, part of UFC contract structure and the sunset clause they used to have, if a fighter was offered a fight and turned it down, the UFC could extend the length of their contract where they had control over the fighter's career. So when Nate Diaz was looking to fight out his contract to go to free agency, he accepted a fight with Khamzat Chimaev, who is the absolute worst possible matchup for him. He was willing to fight him Chimaev to complete his contract.