Sometimes they do when they miss all of training camp and are the only legitimate Top-3 forward on their team. And he'd still be tied for the Bruins team lead.
He scored 36 goals last season as a 21-year old. There was only two other players his age that had at least 32 goals in the NHL last year. Both captained their teams to the Conference Finals, and one won a Cup.
I can understand the defense of the trade, and it may certainly work out to favor the Bruins with the looming first-round draft choices (certainly looks like this year's picks will be outstanding given Toronto's performance), but they'll be fortunate to find a kid with those picks to do the things that Kessel was already doing. Players that hit the back of the net 35+ times a season, which he has the potential to be (at the low end) are hard to find. The Krecji's and Lucic's of the world are not.