When Japanese MMA is evaluated, it is often pointed out that many fighters do not know how to do a proper weight cut. What I would also like to note is that most fighters do not fight in the weight class that is defined by their body frame.
For example, in boxing, Shinji Takehara is the world champion of the heaviest division. His division is middleweight (160 pounds), and he stands 6 feet 1 inch tall. Boxers have a more strict view about fighting at their proper weight. There are fighters in MMA with smaller frames who try to gain muscle for more grappling strength. Therefore, I can't say that everyone fits my theory, but still many Japanese fighters choose the wrong fighting weight.
Motonobu Tezuka fought against the clearly bigger Alex Caceres. After the fight, Tezuka said that he can drop down to flyweight. That makes me think that, when a Japanese fighter enters a major organization where foreign fighters have bigger frames, the Japanese fighter should drop down a division.
That's not to say that every fighter must do so. Certain fighters are not meant to drop the weight, such as the grapplers that I mentioned who bulk up in order to allow themselves to improve their grip on submissions or to maintain position on the ground. Those fighters excel by using their physical strength to their advantage and they would struggle if they cut weight and lost muscle. It becomes risky when they can no longer use their familiar fighting style once their strength is diminished.
There are also many fighters who choose to compete in higher weight categories because there often isn't as much money to be made in MMA's lower weight classes like flyweight, bantamweight and featherweight. Fighting in the higher weight classes leads to bigger paydays. Frankie Edgar, for example, captured the UFC lightweight title even though he only has a bantamweight frame. I am worried that there is too little investment in the lighter weight categories, which limits the sport's potential for growth.
In MMA right now, grapplers need to develop striking pressure to succeed at setting up takedowns at the highest level. Fighter need use strikes to keep opponents off-balance to set up takedowns.
Striking pressure can be made up of a fighter's reach, speed and power, but technique can be used to create space or to close the distance. Striking pressure can be overcome if you take note of distance, angles, combinations and so on. Shinya Aoki did try to do this in his fight against Eddie Alvarez after he had previously lost the pressure battle in his bout with Gilbert Melendez, but due to his lack of power and chin, Alvarez overwhelmed Aoki anyway.
When an opponent has a longer reach, and can adapt to any situation, the fight becomes tougher for a grappler with a shorter reach. This means that divisional flexibility has become much tougher than before.
In the past, you saw fighters trying to submit opponents from the bottom. Once elite fighters learned how to defend submissions from the top, wrestling became much more important in grappling. And now that fighters have become better strikers and have learned how to sprawl to defend against takedown attempts, it is difficult for grapplers to turn fights into grappling matches without first using striking pressure.
Big thanks to Robert Sargent (from MMA Rising) for English editing.