Here are the SC averages of the highest scoring rucks since 2009. I believe the stats are correct as i copied them from this site over the past few seasons. I don't have complete stats outside the top 4 rucks.
2009:
Cox 111
Sandilands 101
Clark 94
Jolly 93
2010:
Sandilands 114
Mumford 93
Bradley 90
Cox 88
2011:
Cox 122
Mumford 115
Goldstein 114
Sandilands 112
2012:
Naitanui 114
Sandilands 113
Maric 113
Cox 112
2013:
Minson 114
Goldstein 114
Kreuzer 98
Leuenberger 97
2014:
Jacobs 115
Mumford 114
Martin 111
Sandilands 108
2015:
Goldy 129
Martin 111
Jacobs 108
Naitanui 104
2016:
Gawn 118
Goldy 108
Naitanui 106
Mumford 99
2017:
Kreuzer 110
Ryder 103
Martin 98
Grundy 97
2018:
Grundy 130
Gawn 127
Martin 105
McEvoy 102
Some reasons for the more drastic changes in the top 4 from year to year IIRC are:
2015 - I have Sandilands 4th that year with 107.5 and Mumford 5th
2017 - Gawn & Goldy injury affected, Naita missed the whole year with injury
2018 - Kruze, Ryder injury affected
2011, 2012, 2014 and 2015 were very strong years for ruck choices with 8-10 players going over 100 each year. So only picking the top 4 players in those years can be misleading because in a lot of cases the guys that dropped out of the top 4 were still close to it the following year.
I think just isolating a top 4 movement can make the situation look more dicy than it really is. When you look over the year on year averages for the core group of premium rucks you see mostly a trend of averages > 100 unless their year is injury affected. In some cases they move up and down by 5-20 ppg without an obvious explanation. But the really big dips are mostly explained by injury.
Interestingly from 2009-2018 there are only 14 rucks in total that ever went over 100. Of those only 10 managed it more than once. Of those only 10 have ever gone over 110. Only 8 went over 100 more than once AND went over 110 at least once.
The "elite 8" are Cox, Sandilands, Goldstein. Mumford, Naitanui, Jacobs, Martin and Gawn. It's was surprising to me just how short a list it was fitting my criteria. Will Grundy be the 9th? He's already gone over 110 but so far only gone over 100 once.