If his career continues on it's current trajectory, then he may have that level of leverage in the future. But he came in as a young unproven guy, and it seems like they all get pretty much the same basic (terrible and exploitative) contract. Honestly if you think your fighter has legit top 5 potential, I think it's in your best interest as a coach or manager to advise them to go to Bellator or another smaller promotion.
Crush a bunch of cans, get some utterly meaningless belts, and get people talking about you and creating a buzz. Saying you're The Best Fighter Outside The UFC. Alvarez, Lombard, Diaz, Melendez, Shields, etc. all got a MUCH better contract than if they'd started out in the ufc. Then either way whether you're an all time great or a washout, you'll still clear high 6 to low 7 figures and get a quicker path to a title shot. Fighters REALLY need to learn that there's more to the fight game than training and fighting. At least if you want to get paid.