Your argument about the timing trade-off is good, but the crux of the issue for me isn't that we didn't get to draft with the picks we gave up, it's that we overpaid
But we didn't, though.
Just go statistically. Here's a great breakdown by Scott Cullen:
http://www.tsn.ca/statistically-speaking-expected-value-of-nhl-draft-picks-1.317819
In case you don't want to open it or can't, he starts off by assigning values to types of players on the 10-point scale. 7 is a top 4 D, and 8 is a top pairing D. Let's start off by pointing out that according to Cullen's model, Travis Hamonic is at least a 7... that's not arguable. I would argue that if he's healthy he's a 7.5 or an 8. He's a great defenceman. But I think we still win this if he's a 7, so let's see.
Cullen goes on to break down the statistical likelihood of players drafted at certain positions becoming NHL players, and becoming good NHL players at that.
No matter how you slice it, players taken in the late first round generally have less than a 30% chance of becoming a 7 or better, based on his analysis. For picks 31-35, the odds of a player becoming a 7 or better is 12.4%. The odds of a second rounder in general playing 100 NHL games, let alone being an impact player, is about one in three.
So, statistically speaking, Travis Hamonic has a 100% chance of becoming a 7, so we can consider him to have a value of 7. The first rounder has (if I'm being really generous) a 30% chance of becoming a 7 or better, so let's call that a value of 2.5 (~30% of 8). The two second rounders have about a 12.5% chance of being a 7 or better, so each can have a value of 1.
So the asset we got for three years at a very good contract has a value of 7, and the picks have a cumulative value of 4.5. And that's being as biased against my own argument as I can be.
I'm interested to hear your logic as to why this is an overpayment.
Of course we could have traded Erik Karlsson and two Jamie Benns for Travis Hamonic. But we also could have traded Tim Erixon, Patrick Sieloff and Markus Granlund. The most objective way to look at value is certainly not to look at the extreme outcomes and ignore the odds of them coming true.