It's a competition - the clue is in the name, it's not the ultimate assessment of martial arts. Let's be clear here there is no such thing as the ultimate martial art and being good at MMA competitions means that - you're good at MMA competitions, no more and no less. There will almost certainly be some crossover and someone who is good at MMA will also be able to defend themselves more effectively than someone who has never trained or trains specifically without contact/sparring of some description but it isn't a complete measure of the utility of a martial art since there are still limitations imposed upon it.
+1.