Defensemen are risky first overall picks compared to forwards, who can be immediate impact players. When you're in a position to pick first overall, that's generally what you need. Compare how Crosby, Kane, Stamkos, and Tavares all hit the ground running for their teams, while Erik Johnson, the fruit of the Blues having had one of their worst seasons in history, spent a year in college, fell out of a golf cart, and generally languished before being traded to Denver for Shattenkirk and Stewart. He still hasn't really made it happen. Subsequent picks in the 2006 draft: Jordan Staal, Jonathan Toews, Niklas Backstrom. Oops.
The Carolina Hurricanes won't even draft stay-at-home defensemen as a matter of principle because they don't trust them not to bust in development. It's a pretty shitty principle, because they miss the playoffs every year, but it goes to show that teams get gun-shy about defensemen with early picks.
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Molly Lambert wrote:
The future holds the possibility to be great or terrible, and since it has not yet occurred it remains simultaneously both.