I have to reiterate that I like Blind as a player. I think his reading of the game is excellent, and his use of the ball is very good. Good passing range too. But that alone is not enough to convince me of his ability at DM. In fact the only evidence we have of his ability in that position, other than for an Ajax team in a very weak division, is when he played there for us. And the general consensus, mine included, was that he was a liability in that role.
That's no shame on the player, but DM is very different to CB, despite how much people like to conflate the two skill sets. I am not ruling out that his time at CB will have helped his physical deficiencies, because he previously looked too weak for the role. And again, I'm agreed that it's impossible to know without experimenting with him there.
Yet, what we do know is that he doesn't have a great history there, whereas he is good at cb and LB. I'm not convinced of the merits of such an experiment, and would rather buy a specialized deep playmaker to replace carrick. The idea that DM is Blind's "premier" position doesn't hold much water. He's barely played there since his early 20's. All his best career performances have come at CB, LB and LWB (Netherlands).
While, on paper, I understand the argument based on his apparent skill set. I remain highly skeptical of his ability in that role, and very much doubt we'll see him there. Skepticism, of course, is not a declaration of fact.