[DEFCON]

i wouldnt say its the most important part, but if you are gonna be a mma fighter you better learn how to effectively fight from and in the clinch positions. I dont think you can pin it down to just one thing thats the most important aspect of mma. Hell striking is a must to learn, I mean if you cant strike nowadays you are at a big disadvantage. On the other hand, if you have no ground game such as wrestling or JJ you are also at a big disadvantage. You could also argue that haveing takedown defense would be important to have as well as the clinch positions. I think the most important aspect is to be as well rounded as possible so you will be ready for anything that should happen in the fight.