He probably should have played college ball one more year, but who can blame him for coming out when he was a top 5 draft pick? He should have fired his agent when the agent held out WAY too long on Heath's contract. That put him behind on learning the offense, and he never caught up. Then he had some kind of foot injury that prevented him from playing again.
He had a shoulder injury (throwing shoulder) that would not get any better.
You are right, he should never have held out. That has been a problem that so many promising rookies have never recovered from.
I watched him as QB many times and my take was he wasn't smart enough to play QB in the NFL. I guess he was alright playing in a wishbone offense, but Gus Ferrotte ate his lunch when it came to making decisions with the ball.