Erk -- you're right. Then you do kind of have to pull in Leveon Bell's deal as a comparable (and David Johnson's, too). However -- Bell's Pittsburgh numbers were greater than Kamara's. The counting stats, anyway.
Really, Bell & Johnson signing bonus paired with Freeman's base salary, with a salary bump for the deal being signed 3 years later ... then negotiate it back down (some!) based on lesser counting stats, the 2019 letdown, and the prospect of more guaranteed money in the deal. That's a starting point, at least. I get back to that 5 yrs for $52 million figure.