let's take a look at those advanced stats you are talking about, ok? All stats are 5 vs 5
Out of all regualars (forwards) around the league, no Line has started less in the offensiv zone than our 4th line. Bollig, Krüger and Smith are #1,#2 & #3.
Out of the Top30 that starts in the D zone Krüger has a worse Corsi than Bollig, Derek Dorsett and Stephen Gionta. That includes the likes of guys like Gionta, Plekanec, McClement, Stajan, Gaustad and 3 million Gordon.
10 guys of that Top30 see a better SV% while they are on the ice. Those guys have Price, Harding (in Beast mode), Lundqvist and then you have 2 guys from TOR and CAR.
About what you say that he faces average opponents... he is the 5th forward on the Hawks when you look at Quality of Competition
In other words, he plays against good competition ONLY and still manages to be one of the best Defensiv forwards in the league.
If you bring up Advanced stats, be sure you read them right or that the other can't read them.
This line also has a good number of Off. zone finishes compared to Off. zone starts. They earned more ice time, especially Krüger with his much improved play.
While we look at stats, he has 18 pts so far while playing on the 4th line only and with the likes of Bollig- who many think should be off the roster.
Being on pace for 30 Points while playing on the 4th line with Bollig and on the PK is really good offensiv production. Being a + Player helps too and him winning faceoffs is another reason. His hard work pays off. I wish some other players would play more with his heart and work as much as him.