I had that thought last year as well, but there is a big difference between catching the ball out of the backfield, and catching the ball in the slot.
As a RB catching balls out of the backfield he will have a LBer covering him 95% of the time. Riddick will win that battle easily.
if he is moved to the slot, he will be up against a Nickle corner the majority of the time. I dont think he would be as successful there (he would still be fine I think, but not as effective as he is in his current role)
No way he makes $4.5m/year
Id say $2.5m is fair