Only if you accept the assumption that the scouting is done properly. Plenty of elite talent has fallen through the cracks. Foster is a perfect example. He's one of the three or four best RBs in the NFL (2nd, in my book), but he wasn't drafted for reasons that were not related to talent.
We'll see how it pans out for Keenum, but the talent evaluation on him was wrong, and continues to be wrong. His arm is just fine, he has more athleticism than many starting QBs, and he definitely has the drive, work ethic, and mental capacity for the position. The only real question was/is experience. He played in a weird system at UH, didn't take snaps under center, and didn't face NFL style defenses. So it's fair to question if he can conquer those challenges. I think he can, but we'll see. But I think any question of his talent is off base. He may not be as talented as guys like Peyton Manning and Aaron Rodgers, but he's more athletic than Schaub. His arm is at least as good as Schaub's. His mobility in the pocket is better than average.
I don't see the knock on talent. Unless you count height as talent, and even then, it's not like he's getting balls batted down or missing reads.