3 goals and 4 assists in
25 games. The cup run was 25 games. And he scored 7 points. You can't take out the other games just because he sucked so much they didn't want to play him.
Whatever you want to say Kessel's deficiencies were (however wrong you may be), Seguin had the same deficiencies during that run, only 10 times worse.
He was basically a Kessel-lite, in every way, with less actual skill and no development.
This has nothing to do with people being "upset about Boston winning".
The cup is not the same thing as the trade. You don't win both, or win neither. They are separate entities.
Getting drafted onto a good team because of a unique scenario does not automatically make you a good player.
Winning a cup does not automatically make every transaction done in the history of the team, good.
Leafs won the trade. Get over it, and go back to the Boston board.