Vestergaard showed a lot of promise in Germany during his early career, but he was never a well-rounded player.
I consider him in the same bracket of defenders as Zanka, Gravgaard and Krøldrup. All perfectly solid defenders but with serious limitations.
Vestergaard was the weakest link in the latest Euro campaign and he hasn't had a sniff since - which is very similar to Zanka who has always been on the fringes too. The others ahead of him have clearly been better, but I wouldn't consider any of them top class except maybe for prime Agger.
So I don't quite agree with you that he would be a starter for nations at the same or higher level than Denmark.