I think Kessel was underrated because Burke made a bad trade to get him. Kessel is good but not as good as Seguin + Hamilton.
He was underrated because he wasn’t given proper credit for what he was able to accomplish with little help. Non-Leafs fans use to rip on him and bash him relentlessly, and used the articles written by Simmons and Feschuk (Or Ron Wilson quotes) as some sort of proof he was as terrible as they all claimed. Narrative changed real quick after the trade though.
But even now there are dopes who don’t know any better claiming he was asked to be the leader (That was Phaneuf), that Toronto media hated him (a few writers), that the fans hated him (he was loved) and that he hated Toronto (he loved Toronto).
He was underrated and disrespected by some people who themselves aren’t liked by Leafs fans, and likely by a lot of the same posters who now sing his praise, at least now he’s being appreciated by people outside Toronto.