... just confirmed my thinking with #1 Son.
He agrees the statement about not joining Kinetics is bollocks.
His opinion of the Kinetic to Static statement is that it shouldn't say "Never"
On the Heavy Recovery Courses they do make a point to discuss the issue that Extensions are often rated or matched to the vehicle winch capacity and that when joining any recovery gear that extra attention be paid to the ratings of all components with the kinetic component/s being the lowest.