That an interesting comp, if we call prime Sundin 1997 to 2002 (in reality it could have been 1993 to 2002 and it is just that the quality of top end center went down making Sundin looking better and better, like for Sakic and Modano)
Sundin was:
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Second in points among center, first in goals, more than doubling in points any leaf of that era, not as large of a volume, but .92 ppg in playoff scoring pace for that time, that Fedorov, close to Sakic. It was 4th among center with 30 playoff games or more and his +20 in only 48 games was really impressive, arguably the best.
85 to 90 Gartner was 5th in points, third in goals among winger, but .82 ppg in the playoff for that era was middle of the road, which would go toward my feeling, when it get really really thight, high level hockey, Sundin superiority (and ridiculous tool that was his 6 foot 5 body) show up to a gear that a Gartner level of player did not have.