I always thought Blind was never really allowed to develop at United. When we first signed him, he was a holding midfielder with a fantastic long pass. Then LVG had one of his daft ideas to slot Blind into the central defense because he could not be bothered to sign a proper central back. Then Mourinho came along and shifted him to LB as cover for Shaw.
It's no wonder he failed to win a place in the team when he's been assigned the role of emergency solution. When the media started writing about Pogba demanding to be played in a role that he felt suited him best, everyone got on his back, claiming he was arrogant and spoiled and that it was no business of his to demand a position to be played in. Well, I think Blind is an example of what happens when players humbly obey whatever managers tells them. I think he could have developed into a great defensive midfielder. Perhaps not to the level of Kante or Keano, but definitely a very good one. He was aggressive, he could produce great tackles and was all over the place. And he could pick out a pass. With time, however, these qualities started to fade and he turned into a mediocre player who was forced to play in roles that did not suit his skills at all.
I surely wish him all the best at Ajax and hope they will help him rediscover his talent and abilities as a midfielder.