Right now, no. Kongo has been stedily evolving his game in his last few appearances, showing an ability to take fights to the ground and hold his own. Before, all he would do is hold on and wait for a stand-up. He showed a sweep or two against Herring, but Herring would just sweep him back. If he continues to evolve his game, and incorporate a little bit of jiu-jitsu, he could be a force to be reckoned with.
I don't think we've seen the best out of Kongo yet. If he keeps training with Rampage and Bisping in England, he can only get better. He is an awesome physical specimine, and the resources he is being given will make him very dangerous. He could very well be a legitimate threat to any UFC HW in the near future.