One of the most difficult things for an athlete to do is to change the perception people had of him when he first came to their attention.
Take the case of Roger Staubach. Roger the Dodger took the sporting world by storm when he won the Heisman Trophy for an unheralded Navy team in 1963. He did this as much via running the ball as he did by passing (he averaged 14 rush attempts per game), and in doing so garnered a reputation as a scrambling quarterback.
Over the course of his pro career, Staubach averaged 3.1 rushing attempts per game. To put that into perspective, Staubach ran the ball roughly one more time per game than Ken Anderson and Joe Ferguson, Staubach contemporaries who both were known as pocket passers, yet he couldn't shake the perception that he was a runner. He had made that reputation in college, and anything he did after that was going to be viewed through the "scrambling quarterback" prism.
Joe Flacco is struggling through a similar type of misperception of his skills. It is thought by many that he is a superb game manager who has yet to make the jump to being an elite passer.
However, a closer look at the metrics shows that Flacco has already made that jump. In fact, they show that Flacco displayed a Philip Rivers-type ability to get his team's vertical passing game in gear regardless of the talent level of his receivers.