I doubt that dollars relative to what we might call average dollars per year was the major sticking point. As I've read some good articles from current and former agents and GMs the consensus is that both parties knew about where this would go regarding overall money per year, as expressed in percentage of salary cap that the player would eat up (which, btw, is why the Raiders admittedly never got serious with Mack).
I suspect that the total number of years was sticking point 1 and total guaranteed money was 1a. Why? Because for Donald, getting another bite of the apple at 30 or 31 years old could have been very beneficial if you are willing to bet on yourself; and AD is that kind. He's the kind of player that, barring a catastrophic injury, will play in top form into his early 30's and maybe to 35 because a) his technique is near perfect, and b) he takes such good care of his body and is so mature in his lifestyle (ala Whitworth).
Just as he could not have received the kind of dollars 4 years ago as he just did because of where the salary cap was, the money he could possibly receive 4 years from now might make this deal seem low if the projected cap of $220 mil comes true. But since this contract keeps him a Ram until he's 34 years old, then that 3rd contract at even bigger bucks isn't going to materialize.
For the Rams, guaranteeing that huge amount of money is a risky commitment in a game that not only is violently played, but even offers risk in non-contract drills. If that catastrophic injury or series of injuries happens and he either is constantly unable to play or he's never the same player again (ala JJ Watt) , the Rams are stuck with an unavailable player or a limited player getting paid mega bucks and releasing him only creates enormous dead cap.
So I imagine that it was the confluence of those two points.... guaranteed money with years of the contract.....where they had to find common ground to get this deal done. The Rams had to give in on guaranteed money, and AD had to give in and sign a max term length contract.
