I'm sure you are familiar with the expected save % based on shot quality:
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xSv% = the save % an average NHL goalie would have, if he faced the same quality shots
dSv% = percentage below or above an average goalie
xSv% shows that Oilers have one of the top teams in limiting high danger shots.
This will automatically make the goalie look better, even though it's the players that are closing down the "red zone" area that Hitch talks about. That being said, Koskinen has done excellent (way above average), even with the low quality of shots.
edit: Note that this list is arranged based on the expected save percentage (shot quality), so these are not the best goalies, but rather the best defensive teams and how their goalies have done.