Who is the weakest UFC Champion right now?

Obviously brock no question, his skills are the weakest out of all of them....bj penn back on top after beating a mean kenny florian, gsp and silva enough said, machida a close second not because of his skill because he is a beast, but there is so much competition in light heavy like Rampage who is about to most likely beat Rashad evans. With that said who can take Brock?? with his size, power, and suprising athletic ability it might take FEDOR to take him out. or the winner of TUF 9