I've said this before about a number of players, but I think an underrated part of what makes a good player is getting on the ground consistently.
e.g. Nicnat is a great ruckman, but given his record of the past few years, there would be plenty you'd take ahead of him, just because you can be fairly sure they'll give you 22 solid games.
We all hope the good players stay injury free, and nobody can predict such things with complete accuracy, but realistically, the likes of JK, given his age and recent injury history, you wouldn't be putting down any large wagers on him playing 22 games of H&A footy. Given that, while some might consider JK to be the better player, you need to ask yourself, would you prefer 22 games from Jack (who almost never misses a game) or 16-20(likely?) games from JK?