You actually defeat greater competition in 2 UFC title defenses.
However, for me, there are tons of UFC champs with 2 title defenses: Lawler, Brock Lesnar, etc. That's an incredible accomplishment. However, I merely regard them as great fighters.
Guys that won the GP, like Wanderlei, Mark Coleman, Mirko Cro Cop.. I regard as legends.
It's just not the same though. What is it about the GP that makes it such a great accomplishment?