I'd have to disagree. I'm horrible at tanking and yet I'm still able to pass these job quests somehow. Regardless, I for one do these job quests just to see more of the side story quests, and not having to be in a group to progress helps a introvert like me find value in this game. If someone is terrible with their class, people WILL let them know just how bad they are, and believe me that's incentive enough to get better. ( I speak from personal experience of course... part of why I hate when they force you to group with others to progress the storyline... actually made me quit the game entirely a couple of times.)