Remember the styrofoam helmets that did not have a plastic coating. Helmet manufacturers saw the increase in rotational brain and neck injuries that those helmets caused. They quietly changed the design, putting the plastic coating on to reduce such injuries before they got sued out of business. Now if they would only take the next step in safer helmets.
Safest - avoid the collision
Next safest - tuck you chin to your chest, do a shoulder roll, etc. so your head does not hit the ground
Least safe - rely on your helmet to save your brain