All it illustrates is that there are other players on the team that are given priority for those roles. He's not a great fit for Rod's PK system compared to guys like Staal, Martinook, Aho, and Jarvis, and he plays behind a bunch of guys on the PP. That doesn't mean he can't fill those roles, he just doesn't in Carolina.
He can only produce in the ice time he's given. Of course he's not going to pile up a ton of PP points when he's only on the ice for ~15 seconds of controlled zone possession per PP
The term "2C" or "3C" refers to where the player slots at 5v5. His production rates alone over the course of a 4 year span put him firmly in middle 6 territory. He's not really utilized much outside of 5v5 (aside from the last 30 seconds of the PP, where the team usually has to regain the zone before anything happens), but as I alluded to earlier, that doesn't mean he's incapable.
He's really exactly what the Devils need. We have our special teams already pretty much set, but we really need a solid, responsible 3C who can win faceoffs, play physical, and produce at 5v5. KK does all of those things and is still only 24. He's very easily worth 5M.