"Will always" is a poorly thought out statement. It's obvious you have zero foresight that there will definitely be dry times for boxing and MMA alike in the future, and it wouldn't be illogical to assume that their peaks and valleys won't match up timewise.Boxing superfights will always trump MMA superfights when it comes to tickets and PPV.
No MMA fight will ever come close to Mayweather-Pacquiao PPV gate or PPV buys. Never.
Of course, you can always retreat to that it's not a boxing superfight if it doesn't beat every MMA fight.
Yes, maybe no MMA fight will ever come close to Mayweather-Pacquiao. But guess what, no other boxing fight has ever been remotely close to that buyrate either, including Pacquiao's and Mayweather's collected back catalogues. Mayweather's next fight after that one did an estimated 400.000 buys, Conor would smash that in any MMA fight. Too bad he's going to embarass himself sportwise.