Ok, numbers speak loud and clear. So, lets ask the question that should have been asked , that being, how bad a mistake did Boston make ? Then there's the first and foremost, how could a team give up what the leafs gave up knowing full well that they would have to " add complimentary players"? Kessel is now a leaf and Carlyle will teach him now, the short coming of Wilson called "defense".
A couple of followup points:
Kessel had made it clear he wanted out of Boston so Chiarelli had to move him. Getting draft picks for a player like Kessel is a bit of a crap shoot. At the time the deal was done it did not look like the pick would end up being 2nd overall so it worked out okay for Chiarelli as he got Seguin.
The deal has worked out for the Leafs as well as they have the premier scoring winger that they really need.
I would call that deal a win/win deal. Some would differ but at this stage I see it as a win/win. Kessel can easily become a 50 goal scorer and Seguin and Hamilton may well prove to be solid NHL players. If either things fail to happen it may change the historical perspective on the trade but as of today it is clearly a win/win and the deal was done three years ago.