If $y is the useful PoW, would that not make $y the scientific reward while $z is the (monetary) token reward by way of mining?

Edit: silly question on my part. y and z should be trivially interchangeable. Your argument appears to rest on the idea that the monetizeable scientific worth of the work would dominate the worth of the crypto token itself, since there would be limited value in an already-mined result beyond standard blockchain speculation - is that the case?