This is one thing that doesn't get discussed much regarding Punk's UFC "run." CM Punk was considered relatively unathletic and somewhat uncoordinated even in pro wrestling. Now, he was undoubtedly a great pro wrestler because he knew how to talk, tell a story in the ring, and structure a match. You don't necessarily need explosive athleticism in pro wrestling and Punk certainly never had it. He was always tough though. For example, he fractured his skill during a match in 2002, finished the match, didn't take pain killers because he's "straight edge," and then only took two months off. Plus, every wrestler is tough just for getting bumped around nightly and working the grueling schedule they have to work. I think we see this character in his fights: a tough, albeit un-athletic and unskilled fighter.
Punk grew up a nerdy pro wrestling fan who never participated in sports. He didn't want to be an athlete, he wanted to be a pro wrestler. He understood pro wrestling very well and was super talented at it. I wish he wasn't so bitter towards it because that is his calling more than anything else.