This is over stated. Defensively there isn't as much difference between a Gagner and a Kane than people would think. Gagner didn't have elite D back sheltering him or a linemate like Toews. He NEVER had that here. He NEVER had sheltering. Really of any kind. 40 games into his career he was being a go to offensive weapon and playing with a rookie, Cogliano, and a career floater in Nilsson. This essentially was his tutelage. Heres the NHL kid, heres the keys, go out and have fun getting drilled into the middle of next year. I can't count the number of times in Gagners first few seasons that he was literally sent airborn. Kind of amazing he wasn't critically injured before he was.
While I agree with a lot of what you are saying, he certainly wasn't sheltered, there is a big gap between our basic evaluation of Gagner. Its an agree to disagree situation as I believe we have had this conversation before.
Kane is a winger. Gagner was used as a center. He absolutely was too slow a skater and thinker to be on the right side of the puck to the extent required as a center. He also was too slow/small/weak to backcheck, help break up cycles, win puck battles and clear the zone.
Not to exaggerate but he was a turn over machine through the nuetral zone when attempting to carry the puck and while extremely willing to battle had an abysmal success rate while doing so.
I think for me. I was a supporter of Gagner, but year after year of watching him take 2 steps forward and then 2 steps back eventually made me dislike the player fundamentally. I saw significant flaws in the way he played for long stretches.
Gagner has talent. Can dangle and snipe. At times did think the game well. But if there is one thing everyone should be able to agree on is that he is incredibly streaky. For me his bad outweighed the good primarily because of his usage. If the Oilers developed him as a middle 6 PP specialist winger with 2 linemates that had speed and defensive responsibility he would have had far more success.