What will happen is tension will be created between Paramount+ and the UFC. Paramount+ will start drawing 10-20 million views for big shows and making tons of money from ad revenue, and the fighters will demand more pay. The UFC will refuse. So any popular champion that can afford to sit out will do so, until the UFC meets their demands. This will result in far more "slop" cards that draw fewer views. At that point Paramount+ will demand the UFC come to terms with their star fighters and put on the best cards they can.
Their contract almost certainly requires the UFC to make good faith efforts to put on the best product they can. Paramount+ didn't give them $1.1B per year so they can just put on slop cards. There is likely some arbitration clause if the UFC fails to meet their obligations.
I think the UFC is going to be forced in arbitration to hand out a much larger % of their $1.1 billion + gate annual revenue to their fighters, in order to put on the best product they can to fulfill their Paramount+ contract. Now, it is a bit more complicated than that. What will actually happen is that arbitration will award damages to Paramount+ for lost revenue due to the UFC refusing to come to terms with their popular champions, and that in turn will motivate the UFC to pay their fighters.
The UFC really signed a bad deal for the scenario that the UFC becomes incredibly popular on the "free" streaming model.