Charlie has shown that he's an excellent caretaker of inherited talent and an effective recruiter. What he hasn't exhibited, as yet, is an ability to motivate, galvanize and coach at the college level.
I don't think it as cut and dried as you present it, here. The team has definitely underachieved in the past few seasons, yes. But how do you explain the turnaround of the offense, between Willingham's last year, and Weis' first? It was almost exactly the same personnel, but the production vastly increased. Mo Stovall went from being an underacheiver, to being an NFL player. Jeff Samardzija went from being practically non-existent, to being one of the better receivers in college football. Brady Quinn went from being incredibly mediocre, to being a first round draft pick. The offense averaged 345.5 yards and 24.08 points per game in 2004. In 2005, they averaged 477.33 yards and 36.67 points per game. They played essentially the same schedule, as well. In 2004 they played Boston College, they played Syracuse in 2005. Other than that one game, the schedule was the same. All of this points to the fact that Weis CAN successfully coach at the college level. He (his staff) certainly hasn't done a consistent job of it. Perhaps that is the result of trying different things each year, to see what works and what doesn't. And perhaps it is the result of pure dumb luck in the good years. But to say he hasn't exhibited any ability to coach, motivate, etc., at the college level is subjective, at best.