He's a legend in the form of a pioneer with excellent ground skills. He's not the end all and be all, even in BJJ tournaments. Hell, even Wallid Ismael beat him on points.
Bas Rutten lost because he's a mediocre fighter with a pancrase background. Like Ken, he was all hype used to sell tickets. And Frank killed him in a Pancrase match because you can't close fist strike. It's an open palm. Frank laughed at Bas when he was hitting him in the head. His striking isn't even anything to write home about.