People underestimate Mirko's ground game. He's a BJJ brown belt. Granted his style is extremely defensive, and he's far more likely to hold you in his guard until the fight is stood up than he is to submit you.
There's no doubt that his Jiu-Jitsu is better than Kongo's, whether or not he will pull of a submission (he has one sub, a standing guillotine, and 3 other verbal taps(subs), one due to leg kicks :P).
He's got some decent ground and pound however, and if he took Kongo to the ground there's a decent chance that things could end with a TKO.
On their feet, I believe that Mirko is a better striker. He did well in K1, though there were quite a few who were better. The thing is, his style of standup was a better translation into MMA than the other K1 fighters.
I still believe that he is one of, if not, the best striker in MMA, despite a dissapointing loss to Gonzaga. Gonzaga is very good, no doubt, but if you've followed Mirko for any length of time then you'll agree that he was just not himself in that fight.
Mirko has experienced some pretty unlikely losses in the past, and each time has come back on a brutal rampage, kicking off heads left and right, and I think he has it in himself to do it one last time.