I think part of it might be that the league mentality has been gradually changing over the past few decades or so. Back in 2010 when Gudbranson was taken with the third pick, maybe some GMs were still looking for that tall, physical, stay-at-home defenseman, and he fit the bill. Although his junior stats weren't all that impressive, either -- in his two OHL seasons before he was drafted, Gudbranson only scored 5 goals in 104 games, and still played to a minus-5.
So it looks like Florida reached with the pick, then for some reason Vancouver signed him to a 3-year extension just last season, and now somehow the Penguins have traded for that contract. Important NHL people continue to see something in this guy.
What I saw last night is a player who is scared to carry the puck. As soon as the puck gets to his stick, he's looking to get rid of it, usually immediately to his defense partner. To me, that's not a good sign. Quality defenseman are able to hold onto the puck, assess the situation, and take the best option available. Guys like Dumo and Schultz have their heads up, take their time, and know where to move it, but they will take the open ice when it's available.
He also got blown by with speed on a couple of occasions, and Pettersson was coming over to help, overcompensating and putting himself way out of position in the process.
Now Gudbranson is a minus player on all three of his NHL teams, and my first impression is I can't really see that changing going forward.