Yep, he's done at 21 
Lot's of players are busts at 21. It happens.
Timothy Beckham and Matt Bush come to mind.
Bryce Harper is his own worst enemy. He has no idea how to calm himself down. His emotions own him. In three seasons, he hasn't learned what to do with pitches outside, nor what to do with breaking balls.
His ceiling is a poor man's Josh Hamilton. ~.275 average, with 25-30 home runs. While nice, he's nothing to get excited about. He damn sure isn't a prodigy anymore. He isn't on pace with the greats like he was even last year. We would be ecstatic if he becomes JD Drew.