It's a little hard to quantify, which I don't like, as quantifying has always been my best mode of explaining things.
It's all tied up in a big messy ball of:
Overpriced players, and trying to workout how overpriced they are.
Over popular players, that are appearing in more teams than their chances of success would indicate they should.
The Rucks being a game within a game, in both AFL and SC. They are not subject to the same grading in structure in SC as the other 3 positions, as their limited number, and potential scoring, force them into a bracket of their own.
The Ruck position having the most inconsistent history in SC.
The Rucks seemingly being the position most likely to miss games.
The perennial problem of SC perception v reality.
The higher any player scores in any given season, the higher the average punter expects them to score the next season. Some might say that is human nature, as they are just reacting to the most recent history. I'd rather look at trends first. I call it "The Icarus Affect". The higher a player flies, the more likely he is to crash, and the higher he flies, the harder he crashes. The last Ruck I really applied it to was Goldstein, coming into the 2016 season. He averaged 129 in 2015, and pretty much nearly everyone on here was labelling him the next SC God, and a must have. I expressed doubts that he could go even close to backing that up. Those that disagreed wrote things along the lines of "at the very worst, he drops to 118-119, and is still clearly the number 1 Ruck, and an absolute must have." When asked, from memory, I said I thought he might drop as low as 115, or even lower. It seemed crazy to pay what quickly becomes a 27 point/$135k premium for a player, and that was if he reached the 115 ceiling I predicted. He didn't. He ended up clearly the number 2 Ruck for the season, and 10 points clear of any player with 20+ games that finished behind him. But would you pay the starting price of 129 to get a 108 player, even if he was clearly 2nd best? With the natural drop of close to 10% by mid season, and 6-7% by round 5/6, it means you would have paid around $150-160k more than what you should have, for the return.
Throw all that into a mixer, and what you come up with is this:
We have 2 Rucks that completely dominated last season. They scored a combined 44/258 last season.
If Icarus flew that high, he would have been dead from heat stroke long before his wings melted!
Let's look at the best two 20+ game Rucks in recent history:
2017 Kreuzer/Ryder 42/213 - (2018 they went 28/170)
2016 Gawn/Goldstein 43/227 - (2017 they went 32/187)
2015 Goldstein/Martin 41/238 - (2016 they went 41/198)
2014 Jacobs/Sandilands 43/223 - (2015 they went 42/214)
None of them even in the ballpark of 44/258! (and look at their follow up years. Games and averages well down! 3 of the 4 are down by 40 points!)
So rather than try and toss a coin, and bet against one, and back the other, I decided it best to bet against both. Depending on how hard one of them falls, if one does, then backing against both is still probably in front of backing both, and one does fall considerably. I don't agree with the premise, that it will take 3-4 trades to get them in. I do however concede if both fire to somewhere near their 2018 level, my season is cooked, and I will struggle to make top 5,000. Against that, rather than run with the majority (I can see at least 50-60% of teams having one or both Grundy/Gawn), I will again tread the path less taken.
Not taking them places another solid (hopefully!) Mid in my Midfield, as against those that are struggling with $500k bet on a hopeful improver at M5. It also adds another Prem into either my Fwd/Def lines, plus a little cash left over. I saw your post expounding the $800k saving on cheap Rucks over Gawn/Grundy. In my current team, that number is closer to $900k, so that extra $100k really does open up the market on the alternatives!
TL;DR
I find it better to bet against players that have a season out of the box, rather than expect that is the new "norm". The fact that we have 2 on the most restricted line in the game makes the bet even more enticing!