A simple solution for the leaderboard aspect would be rather than
having one whole PK leaderboard, dividing it into a Mob Pk leaderboard and a Tower Pk leaderboard.
I understand this wouldn't solve the whole issue, but it would deal with the seasonal/rewards side of things. It would definitely separate the two forms of pkers.
I have seen a lot of good and thoughtful suggestions, soon enough there will be an efficient solution pieced together.