Whether he is a success as an MMA competitor or not, one thing is for certain: If I was walking through some tough neighbourhood and could have only one other guy with me, I'd take Mariusz any day over 99 percent of MMA's elite.
On the street, in a real situation, immense size, strength, physical durability, and athleticism will preserve your ass much better than having a good "ground game". Much of that stuff can be made negligable in effectiveness when one is huge, powerful beyond belief and willing to bite, chew, claw, etc.