It's 2020 and people are still debating on which "style" is the best for MMA.
MMA has become its own methodology of tools, tactics, and strategies. It is a distinct combat sport.
You cannot just train the various delivery platforms (submissions, wrestling, striking) seperately and expect to transition those skills to the cage.
The evolution of MMA as a combat sport required alterations to most techniques from other combat sport systems. While there is carry over on some things there isn't on others. A traditional Muay Thai round kick done in a ring under Muay Thai rules cannot (shouldn't) be executed exactly the same way in MMA. A wrestlers single leg shot is not delivered the exact same way in MMA. Many BJJ techniques are not executed the same way in MMA. All Boxing punches are done differently in MMA.
The list could go on. MMA is a specific training methodology.