The biggest problem is, there is no way to accurately measure heart and desire. Without which, physical abilities don't carry enough weight to guarantee success. It's the crapshoot part of it. No formula, or methodology exists to eliminate being wrong about a player. Nobody has ever figured it out. And nobody ever will.
Nobody.
Ever.
Of course not. There are no guarantees and uncertainty exists.
Welcome to reality.
There are, however, indicators of the likelihood that the level of uncertainty can be reduced to an acceptably manageable amount and that improvement can be measured. How? Try on the field production both individually and the team as a system.
You mentioned the concept of "immeasurables". Call it heart, desire, whatever terms you wish to use to express the psychological/emotional/mental aspects of an athlete that contribute to performance. Do they exist? Of course they do. Can they be directly measured? No. But can their contribution be observed without the ability to directly identify and measure them? I think so.
Here's an example. Reed Doughty. No measurements of his athleticism, physical skills, attributes, his speed, quickness, maneuverability, size, weight, strength could have been used in any combination to accurately predict how effective he was as a football player. He was an overachiever in terms of how good he played, how effective a tackler he was, how he pursued the opposition. Attribute, if you wish, his performance above and beyond what you might have thought to the "immeasurables" of heart, desire, motor, whatever you want and I'll be happy to say they played a major part in his play even though they couldn't be measured. What I see, however, is that their
effect could be both seen and measured.
That was most certainly observable.
(As an aside, you know what happens if you have an elite combination of measurable athletic skills combined with a top teir high level of the "immeasurables"? You get a once-a-generation superlative player. You get a Sean Taylor.)
One more thing.
You mentioned, rightly, that most personnel departments of NFL teams have more misses than hits during the draft.
So what? Where does that matter?
Think baseball, for example. The best hitters when they are at bat do what? .320-.340 batting average? The Astros' Jose Altuve had a league leading .341 average. You know what that means? That means 66% of the times he was at bat he failed to get a hit. A 66% failure rate at anything sounds pretty lousy if your trying to accomplish something-
except for the fact that was better than everybody else. The mean batting average for all MLB teams during the 2014 season was .251-a 75% failure rate. Basically you are measuring ability to do something where the average failure rate is 75% and you measure your success by having fewer failures than the other guy. Altuve had the lowest failure rate among batters in the major leagues and by that measure he was an outstanding success That is analogous to what we are doing here with the upcoming draft.
What matters is that we improve our success rate, or if you wish, lower our rate of failure to a point that our ability to select NFL worthy players is better than it has been and hopefully better than the majority of the other NFL teams. Period.
Indications are that Scott M. has a likely deserved reputation for have one of the lower failure rates among personnel guys and for that reason I at this point am giving him the chance to demonstrate said ability.
As has been said before, time will tell.