It's simple, really: Hughes traded (some) potential for (some) certainty.
Two picks have more potential - it's possible they will amount for more value overall - but the variance is also much wider. Newhook has more certainty - he's already a NHLer at 22, something that the two picks may never even achieve (or again, completely blow pass).
People are going to then evaluate the trade depending on their belief of how much remaining potential Newhook has vs what are the odds of the picks being worth anything. Colorado piked Mikhail Gulyayev, an undersized offensive D who was a ppg in the MHL, Tampa chose Ethan Gauthier, a ppg forward in the Q. How confident can one be that any of these player will be NHLer at 22? They may, but then again, nobody would be surprised if none of them made it. It's not a trick question, it's just a way to visualize the actual tradeoff involved.
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The more I see Hugues build his team, the more I feel he considers picks to have a lower value than his peers, and that may explain his trading behavior at least in part. We often tend to see and evaluate picks, prospects and players kind of separately, but I sense that Hughes see them as a continuum. For him, the difference between Newhook and a mid first round pick is just 4 years of development. A D+4 prospect isn't a fixed asset, he's just another player on its path of pro development, 4 years in advance of a similar player starting it.
I disagree that he could have achieve the same thing by signing some UFA. UFAs cost more, and their best years are generally pass them. They don't have potential anymore. Newhook hasn't reach his peak years yet.