Tensai didn't have even the slightest bit of significant heel momentum going for him. Indeed, he had a whole bunch of fans with long memories about who he used to be who were dying for him to be used well.
Punk's appeal is in his cutting edge harsh heel style. That's why the cool kids like him. Think back to his last face run and it was very much like, meh he's good but he's lacking something.
Punk is better as a heel, but at some point this year, Heyman turn on him and cause another face turn.
I see Punk ending his WWE career as a heel though.
I say tweener.
That way we get the best of both worlds.