I think most sensible fans would take issue with the notion that there is any evidence to suggest that this pick will not pan out.
For those who think they have evidence X,Y, and Z, well..............Ummm how to say it nicely?
1) he had a very disappointing season in the OHL.
2) he had a poor WJC.
3) he had a poor prospects camp highlighting the same issues he was having in junior last year.
4) his offensive game hasn't really developed since being drafted, and his junior team took him off the #1 PP unit and traded for a replacement.
5) he shows continual and ongoing issues engaging physically and fails to get in front of guys taking the puck to his net. Constant lazy, soft stickchecks on guys skating by him to create scoring chances. This is an issue in his play which was repeatedly highlighted last year and showed up again - badly - in Penticton.
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I think this will probably still be a decent NHL player. But his chances of being an impact top-pairing defender - which is what you'd damn well better be getting at #5 overall - took a substantial hit based on his mediocre performance over the past year. And if you're claiming otherwise, your head is stuck in the sand wearing rose-coloured glasses.