Eh, what does Owens do that makes him incapable of acting like a true heel? Dude is probably one of the better heels on the roster.
Owen toes the line pretty hard. He's often too entertaining on the mic and too dominating in the ring to be a "true heel". From what I can gather, a 'True Heel':
1) Doesn't do anything fantastical in the ring. No impressive moves unless they are power moves.
2) Makes the crowd hate him on the mic -for real-
Owens does death valley drivers, swanton bombs, pump handle neck breakers, and takes clotheslines with inside out sells and DDTs with headstand sells. He's too entertaining in the ring.
Owens can talk so well on the mic and does hilarious yapping in the ring and against Michael Cole. People love hearing him talk, especially when he's being a jerk.
The only time he starts working 'True Heel' is when his ring work is all chops, sentons, and super kicks. And the only time he's 'True Heel' on the mic is when he delivers promos like the NXT "you're the John Cena of wrestling fans" promo. But even then, smarks love him for working a crowd that well.
It's the same as The New Day -- snarky face comedy for 90% of their promo, then tack on a jab at local sports team to show how heel they are in the end.