A MMA BJJ Black Belt will have many tricks to display if he needs them, but he will never be anywhere near a pure BJJ practitioner Black Belt. Like a MMA Wrestler normally should not outwrestle his Wrestling coach.
Of course JDS could submit ppl. This is a shot in the dark statement, but I don't think he is foreseeing or looking for this outcome against Cain.
JDS is a complete fighter, but I would rank his assets like this:
JDS Boxing>JDS TDD>JDS BJJ
I will support your good point regardless of our differences.