I want to also point out that side jobs don't have to be ironically limited to single roles; for instance, Blue Mage is also currently playable as a tank or healer role, not solely a DPS role. Is Black Mage a "limited job" because it can only be a DPS caster? Could Scholar be considered a "limited job" since it's only categorized as a healer? Blue Mage can fill in for any of the major three roles, which is something that none of the other three jobs do to a significantly notable degree... and before anyone brings it up, no, Summoner having a raise ability or Red Mage having a single healing spell is not equivalent in terms of the amount of role-specific actions that Blue Mage has for tank, healer, and DPS roles.
Again, just because a job has unique content and mechanics available to it doesn't mean that "limited" is the best label for it. Blue Mage has a unique method of learning spells, it has a larger total selection of actions that it can choose between, it has access to unique pieces of content like the Masked Carnivale and blue log challenges, and it's less limited when it comes to role assignments since it can be a DPS, healer, or tank.
The label "limited job" in many cases is misleading, negative, and extremely subjective. There's some content that Blue Mage can't participate in, but there's conversely some content that only Blue Mage can participate in, and there are unique gameplay mechanics that only Blue Mage has access to. If this is considered limited, then I could easily make similarly subjective arguments for other existing jobs as well.
