Yeah, I don’t agree with that either. We have seen cases where either classes being added to the game before, along with, or even after the introduction of an npc of whom the class is based on; as well as cases where we had npcs whom hadn’t been used as a mold for new playable classes.
That’s where talents can come in as they can let you specialize in killing bosses. However class systems shouldn’t force players into that role unless they themselves want to play that role.
For example instead of a class system where you can mark single targets for more damage (which again works better for a talent ability); Hunters could instead use a coating system where they can use vials to coat their weapons with various affects. For example arrows could be coated with explosive substance so that your arrows are now explosive arrows, or traps could be coated with venom so that your traps would poison any enemies it hits along with their normal affects. This type of system would offer players additional creativity when building their characters on par with that of the Arsenal and Enchantment system, while at the same time doesn’t relegate the Hunter into a Boss Killer role.