In terms of ability to put up a collective defensive display, I doubt any Eredivisie team is capable of what United did tonight. Attacking-wise, the best Eredivisie teams could certainly do better than this. Regardless, I do not doubt Ajax are capable of a better performance than tonight. The thing is, Mourinho is very good at making a gameplan that makes the opposition look like they're underperforming. I used to hate him for it. He's good at spotting the strong points of the opposition and finding a way to stop that.
Man Utd's problem this season has been to come up with creative stuff themselves - and to take advantage of dominating games. Defensively, the season has been very good with the odd exception.