You do know that the UFC has a different pay model than boxing typically has, right? The numbers that NSAC publishes are only a fraction of what UFC fighters make. Even Rampage makes more than a million a fight we recently found out. GSP is rumored to make between 2.5 and 5 million per fight. Not Mayweather and Pacquiao numbers, but better than just about everyone else and certainly better than Kessler.
I"m too lazy to find the Sean McCorkle thread on the Underground but he went over the pay structure for bottom tier guys and, even for them, the listed purse is a minority of the total pay to fighters.
I hope this doesn't come across as bad mouthing boxing, I just think that there is enough public information out there to progress the discussion beyond: Boxers make a lot of money, MMA fighters don't make any money. At the bottom end of each sport, guys don't make shit--a hundred a round per fight in the U.S. in some cases, even less overseas or in shady events. At the level you start to see them on TV regularly they can probably quit their other job. The guys who are being featured as headliners are making a lot of money, both in MMA and boxing. The only anomaly in the comparison is that the top 1-2 boxers--Mayweather and Pacquiao now, ODLH and Tyson in earlier generations, etc.--have no comparable counterpart in the MMA world.