But thats also picking toward the end of round 1 where the projections are more difficult. RB is probably the easiest projection in the NFL. Thats why they can be found just about anywhere in the draft. Dowdle , an UDFA, was actually one of the better rbs in the league this year. It just took the coaching staff half a season to figure that out. He would have had 1500 yards this year if MM had utilized him in the first 8 games like he did in the final 9 games.
Even top tier rbs are pretty cheap. The top free agents last year were Josh Jacobs and Barkley. Both make around 12-13M per year. The 12th pick makes around 20M over 4 years. So, if Jeanty is one of the best rbs and you don't do something stupid and sign him before his 5th season (Zeke) , you can save around 7M per year vs a top tier free agent. Now look at DE, top edge rushers make 28-30M a year. Top CBs make 20-22M per year. Top OTs make 26-28M a year. They make 3-4X more than RBs.
So, you can see the huge difference in cap value by simply using rookie contracts to pay for these uber expensive positions. Drafting a rb with a first round pick is a poor cap value. The 12th pick needs to be a premium position like CB or DE or OT....... particularly at #12 were you don't really have to compromise your draft board much to take the position of greater value.