The wrestler being at a disadvantage isn't a belief, it's a fact backed up by real life. The guy that I train with has experience in both wrestling and Jiu Jitsu, and knows for a fact that Jiu Jitsu beats wrestling every time. The Gracie family (who more or less started MMA), took on all comers and wiped the floor with every single wrestler that stepped up to take the challenge. No one could beat them until the other fighters started picking up Jiu Jitsu. Power is nothing but a detriment if your opponent knows how to use it against you.

Edit: It's Shien that specializes in creating openings (which despite being under the same heading, isn't the same style as Djem So. There are too many differences), Djem So specializes in overwhelming your opponent with powerful strikes.