None of this shoulder stuff would make any sense to an Anatomy major. If you consider either the right or left shoulder the distal end of a clavicle/scapula bone, then all that you can cause the distal end to do is elevate, depress, protract, or retract, or all of the above in a motion called circumduction, and each of these two shoulder bone complexes can be caused to move in these manners independently of the other clavicle/scapula shoulder bone complex.
Or a shoulder -- as a joint capsule -- can facilitate abduction, adduction, flexion, extension, internal rotation, and external rotation of each humerus bone. Each humerus bone can act independently of the other or they can work together as a force couplet.
A steep or a shallow shoulder bone movement, as a bone or as a joint, relative to a golf swing, could only be identified as steep or shallow based on the inclination of your spine as you rotate your torso and/or move your arms around your spine. Its entirely and utterly ambitious to try to simultaneously understand and explain shoulder motions as bone prominences or joint capsules, or both, during a golf swing. Please Stop!
For my own explanations and comprehensions, please consider the shoulder as a joint and not the bony end or prominence of two big bones that come together as the acromium process.
