Evaluating quarterbacks is incredibly complex, which is why we see so many busts. It’s a combination of factors, and even then, you're trying to project how someone will evolve under pressure in a system that may not suit them.
At a fundamental level, a QB has to clear a baseline of physical and mental traits. Bryce Young, for example, doesn’t convincingly clear either. Physically, you need size, arm strength and functional accuracy. Mentally, you need processing speed, adaptability, and the ability to operate under pressure.
Even if a QB is in the wrong scheme - Rich Gannon in an Air Coryell system, for instance - you should still see flashes that indicate he’s an NFL-caliber quarterback. Scheme fit is one of two key factors that can elevate a QB’s performance. The other is how they mentally approach the game.
And that’s the hardest part to quantify during the draft process. The elite QBs know where every player—offence and defence—is supposed to be on any given play, and they can adjust when things break down. The very best are obsessive about film study and mechanics. Brady flew in his personal QB coach during the season to fine-tune his footwork. Brees completely rebuilt his throwing motion after shoulder surgery.
That level of dedication separates the good from the great.