RB Durability is the main issue here. Its hard to give a man 8 digit salary when the odds say the player will probabaly miss some significant time during the contract. This is changing somewhat, thanks to what we witnessed with Derrik Henry Saquan Barkley, and now Cook and some others.
WR became over valued when the league shifted away from top RBs and used the pass to set up the run, but it appears that the run game is witnessing a resurgence across the league to take advantage of defenses designed heavily at stopping the pass.
I agree the game is won and lost in the trenches, no RB is worth it if the OL can't create the holes, and same can be said about a DL that can plug those holes and rush the QB. I put a premium on the OL and DL because nothing can really work well without solid lines. No matter the phase the league is in the OL and DL have to work well for the offense and defense to work well IMO