Modern NFL Draft Strategy: BPA vs Position of Need vs "Ready to Contribute"

[Chaos]

Tradtionally discussion of draft philosophies revolve around Best Player Available vs Position Need. And discussions how to balance those issues. 

But I don't think either of those or a combination of either of those is sufficent and may not even be the correct approach.  

I believe the correct approach is to focus on how to maximize a teams quality snaps under rookie contracts. Every position of need can be filled in someway in free agency. I don't have the energy yet to quantify this.  An example of the decisision making is to evaluate each player in the draft against the players you have at the same position.  The evaulation is not a simple "does that upgrade the position".  The correct evaluation is  does this player increase my ROI at the position. For example you are comparing Rookie x vs Greg Rousseau.  And you estimate of the course of the next 4 years Groot is going to generate "1000 units" of performance, at a cost of $80 million. I estimate rookie X could generate 800 units of production at a cost of $16 million over the next four years.  Groot costs $8k per unit of production. Rookie x costs 2k per unit of production.  So my calculus on this comparison is, I free up $64 million of cap space drafting this rookie, and letting Groot move on. And I need to find another 200 units of production on the defensive side of the ball. It seems have $64 million freed up should be able to add more than 200 units of production.  So in this example, while Groot is a fine NFL player, and his contract is inline with similar players second contract, it might not be a good investment.  And this analysis needs to be applied to every player on the roster, and every prospect in the draft you think is an NFL caliber player.   In my head, I start stacking those $64 million savings up, to use towards getting some true difference makers. 

I realize this is half-baked, but am looking for feedback on whether anyone thinks there is merit to understanding this "third approach" to draft strategy.