All champions cherry pick. It's different at the top in both sports like that... Boxing taught MMA that holding on the the belt for longer makes financial sense, but I don't agree that top fighters avoid eachother for longer. I think it's about the same time wise, but that's also because of how complicated it is, and there are so many more fighters.
c'mon - the champ in mma almost always faces the most compelling challenger in the world. and that rarely happens in boxing. and generally other top contenders fight tougher ranked fights more frequently.