Truthfully though, if I'm Karlsson I sorta baulk at the "Letang is #1". Realistically, you're probably looking at running both pairings 22-25min and the third pairing <10min. That is what is most tactically advantageous for the team and the respective players. And most of the time you're getting a Crosby or Malkin line. Third/Fourth lines, I imagine they lean on Letang a tad bit more.
And Karlsson running the PP, yes please. As "not smart" as Letang seems at various points in time, it can't be lost on him that Karlsson would be the 1PP QB. And honestly, having Letang and Karlsson as your top pairing on the PP, that's very appealing for a variety of reasons. If I'm Sullivan, I have the sit down with Sid and Geno and tell them that EK is running the show. As the defending team, you're now forced to pick and choose which player you focus on and given the list is: Crosby, Malkin, Letang, Karlsson, Jake? That's problematic. So if you actually commit to a PP system and moving your f***ing feet, we could see a very lethal powerplay.
I can be "A" star and not "THEE" star. I think there's appeal in that. Maybe no different than Kessel back in the day.