I’ve studied the 5 golf dynamics, but lately I’ve been hearing this term of shallowing the club on the down swing. How does that relate to dynamic #5?

Shallowing out the club would relate more to Dynamic #2 than #5. The most important aspect is not depth of divot, but rather identifying the swing bottom. If the swing bottom is too far forward, divots will be too steep, but that is better than too shallow, caused from a swing bottom being too far behind.