I think what people might be missing about "goals saved above expected" is that it's not a measurement of goals vs saves or shots etc... it's a measurement of "expected goals" vs all goals allowed.
What's an "Expected Goal" (xG)?
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The chance of an unblocked shot attempt being a goal. For example, a rebound shot in the slot may have a 50% of going in and be worth 0.5 expected goals, while a shot from the blueline while short handed may be worth 0.01 expected goals. The expected value of each shot attempt is calculated by the MoneyPuck Expected Goals model. Expected goals is commonly abbreviated as "xGoals". Blocked shot attempts are valued at 0 xGoals. The expected goal value assumes than a player of average shooting ability is taking the shot. A player's shooting talent is not factored into this metric. Another metric, called "shooting talent expected goals" is available that does that.
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What is "Goals Saved Above Expected" (GSAx)?
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Expected Goals against minus the actual number of goals the goalie has let in. A positive number means the goalie is stopping more goals than an average goalie would.
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So you take the total of all expected goals a goalie has face, and you subtract all goals they've allowed. If you end up with a positive result, it means the goalie has allowed less goals than they were expected to. A negative means they've allowed more goals than they were expected to.
It doesn't mean that all goals against are considered equal. It means if you allow 60 goals, but only 40 of them were actually expected to go in (based on the above definition of an Expected Goal), then you've allowed 20 more goals than you should have. If you allow 40, but you were expected to allow 60, then you've saved 20 more goals than you should have.
Shot selection, location, etc is already factored into whether an expected goal has occured or not, so trying to argue that "all goals are not created equal" is moot in this case. The stat is already aware of that, and has already factored it all in.
Edit: I don't mean to sound "matter of fact" about the validity of the stat itself, I'm only confident in my understanding of what the stat is and how to apply it (in addition to other factors) in my thinking about a goalie's abilities. I'm more than willing to be convinced that the stat is flawed, but I need logical evidence to support the idea... and the idea has to originate from a demonstrated understanding of what the stat actually represents.
Edit 2: The quoted definitions above are from Monepuck (they also provide a "learn more" link to Natural StatTrick for xGs).