we need a sword dps

[Brian_]

The only current role that actually gives Red Mage the room to perform its entire intended skill-set is healer. And, before someone says "healer? Red Mage is more than a healer!" Healers in this game are more than just healers, too. As a healer, Red Mage would be able to output decent DPS while having the flexibility to do so as either melee / ranged (given that there is no classification of melee healer / ranged healer). And, as a healer, they'd naturally have sufficient heals and party support.

As a DPS or tank, their impact in terms of party support and healing would need to be limited for balance reasons and they'd inevitably be judged purely in DPS or tank metrics. Some examples of this -- cross classed healing in worthless on BLM, SMN, and PLD. Clemency continues to suck. BRD and MCH have devolved into pure DPS classes despite their "support" role. A lot of utility has become marginalized in the pursuit of DPS.

Samurai I feel has a bit more flexibility. But, among the more iconic FF classes that aren't in FFXIV yet, there are very few that make sense as a tank and actually have a strong appeal to non-tank players. Meanwhile, there are a lot that could fit as a DPS. Given that there needs to be variety and balance to the three roles for the lifespan of FFXIV, it doesn't make any sense to make one of your rare few tank flavored jobs into a role that you have a surplus of options for.