Of course it works that way! Perception and information are crucial to battle. Manipulate those and you can keep an opponent convinced that you're the biggest threat on the battlefield, even when someone else might in fact be doing farm more harm.

As for defending themselves, anyone who's lasted in Azeroth long enough understands that principle. But specialization means efficiency! It's much better to have one person who can take the worst an enemy has to offer unbowed while the others strike at it, than everyone trading their offense for defense and no one being able to land a decisive blow.