This is just rubbish. Safety arises from multiple dimensions - Kevlar-threaded armour is a single, last line of defence that helps only when everything else has failed.
Actual safety comes from training, practice and operations - such as understanding how the tool works, what unexpected dangers exist, what techniques to avoid, the state of the immediate environment, prioritising safety (eg by not creating time pressure) and the design of the tool itself (eg chain guards and anti whip mechanisms)
By the time your Kevlar armour comes into play you are well outside the safety zone and deep into the shit your pants zone.
You're right that the kevlar is the last line of defense. Nevertheless, one would be a fool not to wear it, as machinery fails and people make mistakes. There are photos on the intertoobs of shredded kevlar and no injury to the "thank god I put on my armor!" sawyer.
Actual safety comes from training, practice and operations - such as understanding how the tool works, what unexpected dangers exist, what techniques to avoid, the state of the immediate environment, prioritising safety (eg by not creating time pressure) and the design of the tool itself (eg chain guards and anti whip mechanisms)
By the time your Kevlar armour comes into play you are well outside the safety zone and deep into the shit your pants zone.