It seems to me that the preference for AFL teams is to have 2 ruckmen who can share the ruck load. Mike Pyke and Shane Mumford, Dean Cox and Nic Nat, Max Bailey and David Hale, Ben McEvoy and David Hale, Brad Ottens and Trent West. When they can't find 2 worthy ruckmen they settle for the solo ruckmen (like Jacobs, Martin, Mummy and Goldstein last year who become our supercoach premium rucks) with a tall key position player providing a cameo role. Even though these ruckmen are lauded for how good they are the AFL coach still thinks his team would be better with 2 and continues to search and experiment. Could this be one of the reasons it is so hard for the solo ruckmen to have consecutive premium supercoach years? Given this train of thought Sandi and Nic Nat look like the 2 ruckmen least likely to have their role affected as they have already been playing with a second ruckmen. Unless you get a situation where the second and third ruckmen are injured or not ready to play (like Brisbane last year) I think the solo ruckmen's job and scoring is always vulnerable to change.
Just thinking out loud!