I think you are close to realizing that the core does not turn the hips.Ok so to transmit force and distribute strain, the body uses a series of fascial slings and chains. There are six, the back line, front line, lateral line. spiral line. back functional line and deep front line.
these allow muscle contractions to affect another muscle that it attaches to through fascia. There are receptors in the muscles called golgi tendons which respond to stretch. When the muscles fibers of the second muscle stretch, a signal is sent neurologically to the spinal cord which elicits a motor neuron to fire the muscle that is stretched. Thus, a contraction in ‘A’ muscle can help facilitate a contraction in ‘B’ muscle. This is the fascial chain at work aka kinetic chain.
goggle ‘fascial lines’ for a visual.
If you realize that(for a right randed batter) the right leg pushes(by pulling on bones) the right side of the pelvis forward and the front leg stops and pushes(by pulling on bones) the left side of the pelvis rearward you will see how rotation happens. Hip rotation is from legs.
And in the swing this hip roation happens so obliques can pull against.
Hip rotation happens to keep obliques stretched so they can keep pulling.
Muscles only pull.
To argue otherwise is wrong.