Actually your wrong about the ninja in XI, it was intended to be a jack of all trades - tank / dps / support. That's why it had the modes for each, tho your right about how we as players did pigeon hole it's potential into being just a tank.

However, not everyone seeks to complete the objective for the sake of being a jerk some people just want the rewards such as seals or just the feeling of completion that goes along with it. Fates in general are a system that needs serious work this one is no exception.