the fallacy is that a 20mm screw on a 5mm pitch has a minor diameter of 15mm which means the inner bore couldnt be more than 10mm, so the stiffness would be the same as a 19.5mm solid screw and the inertia similarly.. i.e. boring a 10mm hole reduces the inertia by 7%... hardly worth the effort.

On a 40mm dia, 40mm pitch screw the thread minor dia is 35mm so a 25mm bore might be possible... about a 16% reductoin in inertia... might be worth it in some scenarios

but overall, not worth the trouble, which is why you never see them