[YodasLuke]

However, I presume that we both agree that it would not be a good idea to have a forward-leaning spine tilt at impact when hitting a driver.

That's true, unless you've ever played at Kiawah Island. So, your presumption is too narrow. I can lower my launch angle by 8 degrees with forward spine tilt, which could be an advantage in a 50mph headwind.

Yodas Luke

I agree with you regarding those scenarios.

Also, I generally agree with you when you state-: "I could position the ball inside my foot and outside my Left Shoulder (very wide stance and/or too much axis tilt at Address), and I'd have the ability to strike the ball with an ascending blow." However, I think that Jamie Sadlowski has the ability to hit a descending blow under those same conditions - because his left upper arm is well ahead of his left shoulder socket at impact, and he also has a large degree of left elbow bend at impact which moves his left forearm behind (inside) his left upper arm and it also angles his left forearm backwards away from the target.
Jeff.

Then, as you have also shown, we agree about the use of the word "only". And, we also agree that the fulcrum, whether it's the elbow, the shoulder, or the wrist, is the deciding factor in the descending or ascending clubhead. It has little to do with the foot.