You never said anything about fans with knowledge of the game. You said "fans". Go read the comments of any of the Lions Facebook posts after each draft pick and you'd probably throw up. If you want to cherry pick the self informed fans and then have them go up against the GMs, sure, your probability of having a more successful draft goes up. But I'd still be far more confident in the guy(s) that has/have first hand access to the players in the weeks/months before the draft over even the most informed fans that are constantly watching out of town games and reading their fill of scouting reports. They just have an edge that fans will never have.
Was I watching Tomlinson every play during the Duke games I watched? Nope, sure wasn't. But I distinctly remember Duke running the ball pretty well in both games and the Duke QB was well protected in both games as well. You asked how many Duke games I watched, I answered. Then you wanted to know what I watched during the games, I answered. How is this relevant at all? No idea, but there you go.
And I haven't once said GMs, fans, or "experts" are worthless. You keep using that word, but I won't.