You rate WR and RB higher than I do in their level of importance to the team (and therefore the amount of cap space I would designate to the position), so we'll agree to disagree.
I'd certainly hesitate before committing to a league-best contract for a WR, even a great WR, when I'm not sure of my QB and my offensive line is a bit of a work in progress. A star receiver doesn't do me much good if my QB is scatter-armed, or if my passer is lying on his back because my o-line can't protect him. In those scenarios, my star receiver might be wide open in the end zone, but because he's not getting the ball it does me no good at all.
And I'd never pay a RB a league-best contract unless my offensive line was pretty damn solid and set to go. Even the best RBs need blocking.
But... edge rusher is one position we agree on.