I think its primary the 2nd part of the season that he faced this problem, but especially in the start, I have seen him influencing our tempo with passing forwards, dribbles forwards, passes to the side. Especially in the later part of the season, he's been more of a third CB, than a #6 as Carrick is. But I even wouldnt be surprised if this is what LVG wants him to do, Blind spoke recently that LVG wants him to be tidy in possession, distribute the ball and wait for openings, furthermore he's more of a helper of our defence in possession than Carrick is.
He's 25 and its his first season in a new, far thougher league, he started good (people even opting for him as one of our best outfield players), ended far less, looked fatigued, but all in all, I think its a bit silly to completely write him off, and not even want him as a 2nd DM. Especially him, as I've seen him go from barely good enough for Groningen to being arguably one of the best LB's at the WC, he surprises quite a lot.