Is this lift and the associated "snatch" the greatest single test of overall power?

no the single greatest test is deadlift
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it is the best exercise to raise GH levels. its damned hard to do too.
It's a very technical and difficult lift, but a poor test of overall power.
dead or squat
Deadlifts and squats are great examples of maximum strength, not power - at least in the sense I think that the OP is inquiring about. Power lifts = power clean, snatch, etc.
I think he's referring to strength x speed = power. Some people may be able to deadlift 600lbs, yet cannot power clean 225lbs. And people that can power clean 225lbs. may not be able to deadlift 600lbs. I would consider the person who can power clean with the most weight to be the most powerful.
But, this argument can go in circles, and usually ends up being an argument over semantics.