I took your response to mean that the Professional GMs screw up so therefore a casual fan's opinion is just as valid. My entire point is that the OP is complaining about Packer depth, I am was pointing out his (and our) lack of knowledge as well as the silliness of ridiculing TT because of it. Your response led me to believe you were arguing this point.
In my opinion, errors occur usually in determining a players dedication. We can measure a players physical skills, we can test his athleticism; we can watch tape and figure out his understanding of football. But, we are handing a young man a check with more $$$ than his father has earned in a lifetime of labor. How does he react? For some that is the apex of life. They worked hard to get there and the goal is met. With that loss of an edge, they are now prone to mediocrity or worse. This is the most difficult aspect of scouting - will they continue to work when they are rich? Especially these days. The agents know this and a surprising number of recruits have been tutored in what to say for every question.
Your point on the Lions wasting a pick, is clear. But it is also clear you are missing the point about managing risk/reward. Do you think that the Vikings drafting Peterson was a huge mistake? He dropped significantly (down to 7) despite being the top prospect that year and maybe the best RB in quite some time. If the Vikes took him and his shoulder never quite healed and he never played again, would that have been a bust? Its easy to look in retrospect but at the time the GM has to weight the risk vrs how well the player may be.