I'm of this very opinion. He only invites/given a handful of prospects - so they're already presumed to be the best of that class. Within the show is him showing film of the good and bad and gives them advice. Then there's a chalk board session and an outside session. He also gives them an opportunity to answer some negatives that already being said about them, ie, some say you're only a mobile QB, some say you don't have the arm strength, some say you can't operate under center, some say you weren't asked to read defenses, etc. It gives the viewer an opportunity to make their own opinion even though it always ends up with Gruden being positive overall about the player.