Cook has been inconsistent and unreliable his whole career. For every play like that sideline catch he made against the Cowboys you get at least two screw-ups. He's flashy, but he makes Bennett almost look like Witten in terms of reliability.
He had 377 yards all year for the Packers. Bennett had like double that. And that was with Gronk as the #1 TE part of the season and a nagging injury.