Combating a misconception about DPS knowing less by creating a misconception stating DPS knows more is not exactly the best of ideas.

All 3 roles are equally as important, this is fact. But a downed/bad DPS is easier to recover from than a downed/bad healer or tank (because there are more of them) and this is where the idea that DPS is less important comes from. It's as simple as that.

Also I beg to disagree that DPS know mechanics better. It is a player trait if someone can pick up on mechanics easily or not, not a role trait.