Further to what
@Hivemind said, I think pretty much anyone with NHL level talent can be an effective PKer. It’s a matter of choosing which players should be used there vs. saved for other situations such as ES and the PP. I also think scheme and coaching is more important on the PK rather than pure defensive ability.
I think most people would agree that Backstrom is probably their best defensive forward at ES, but he’s behind Beagle and Eller on the PK rotation because why waste his energy on a job that others could do? Not that that’s why Kempny wasn’t used there, but it makes much more sense to play Orpik in a heavy PK role because he is not an effective ES player and has no role on the PP. And Trotz was likely just more content to stick with Orlov as the #2 LD on the PK due to familiarity.