My general observation is that the more layers of abstraction between you and actual metal, the better the pay. Production machinist < CAM < Mech Eng < Elec Eng < SW Eng < ML Eng.

This is a pretty gross generalization. I've known someone who ran single-point diamond turning machines, ~directly working with the metal (or whatever). It is highly specialized and my guess is he made probably mid-hundreds of k$/yr.