How Modern Golf Instruction is Failing Us
The below is an excerpt on how to "swing more athletically" from a popular golf blog:
Excerpt from Golf Blog
When hitting the driver, stand so the insides of the feet match the width of your shoulders. Your stance should narrow slightly when using shorter clubs, but the outsides of the feet should never be less than shoulder width apart.
Flare the left toe toward the target by about 15°. The right foot should be perpendicular to the target line, or flared a touch to the right.
Flex the knees enough to feel balanced and dynamic, but don't overdo it.
Bend at the hips, not the waist, when putting the club in position.
The spine is straight from waist through the neck.
Relax, beginning with a loose jaw (no clinching).
Other elements of an athletic swing include full rotation of the shoulders and hips (ideally, reaching 90° and 45°, respectively, at the top of the backswing), and a powerful coiling and uncoiling of the torso.
Where It Goes Wrong
If you're familiar with the Golf Like An Athlete philosophy, then you know that the foundations of Golf Swing are identical to the foundational movements found in a variety of other sports that involving using your body to move an object horizontally (i.e. swinging a baseball bat, throwing a football or frisbee, a hockey slap shot, etc.).
With this in mind, re-read the above list of suggestions and ask yourself - would this advice EVER be given to someone learning how to swing a baseball bat or tennis racquet?
I've been the recipient of a ton of great tennis instruction over the years, and no instructor has ever indicated that my left foot needs to be 15 degrees out and the my shoulders and hips need to be at 90 degrees and 45 degrees when winding up to swing the racquet.
For another analogy, have you ever seen a baseball player step into the batters box and think about no less then 7 things when they set up to take the pitch? Never, they get into the athletic stance and posture that works for them and swing away.
Applying this to your current journey with the golf swing, is the reason your slicing the ball 75 yards right because your jaw was clenched? Of course not.
All of this "instruction" is a distraction from the real issue, which is that you've never been taught how to move your body in line with the basic athletic principles required to generate horizontal force.
How to Navigate the World of Modern Golf Instruction
When your still learning the swing, a general rule of thumb is to focus on instruction that emphasizes how your body should move (feet, legs, hips, chest), and avoid instruction that focuses on how your wrist and/or the club should move (hands, arms, shoulders, club face).
Just like in every other sport, our legs and core are what power athletic movements. To jump into the golf swing focusing on your hands, arms, and the club would be the swing equivalent of the proverbial "tail wagging the dog".