That depends on your mindset too. Someone playing a rogue for bignumberdpslol is not playing the same role as a dps warrior/paladin who keep taunt and a sword/board swap bound so they can save a pull at their own expense instead of using vanish/feign and the rest of the group is fucked, or a caster that keeps an eye on the other squishies and is fully prepared to throw out all the help they can in case someone gets aggro for some reason.

Knowing how to use your class to control a fight properly is not exclusive to tanks or healers, but it is necessary.