The Pens were 40-31-11 last year with a bunch of injuries and without Karlsson. This year less injuries , Karlsson added and they are .500. My point was that he is not an impact player any more.
So, have you been watching the pens? I ask, because quoting the standings then suggesting he's not an impact player is a correlation based argument rather than one about the players direct impact.
Interestingly, Karlsson's underlying numbers are all pretty strong, the one area the team fell off is actually the pp. Not sure what's going on there, and certainly he should have helped there, but Letang is still on the team so they could have still run their old units if that was getting it done better, suggesting Karlsson isn't likely the reason for the fall off.
I'm also unsure about your claim about injuries, sites that track injuries like NHL injury viz have it about the same last year to this year.
Certainly Karlsson isn't the guy he was in his prime. Neither is Giroux. But is he still an effective player? Well, he won the Norris last year, and is still putting up respectable (quite good actually) underlying numbers this year. If your expecting elite, well he probably wouldn't be available if he was that, but if your expecting a guy that can still provide top pair performance, yeah, he's still that.