See, this would be an argument for such a thing if past FF games had stuck anywhere close to historical Samurai, but they don't, not by a long shot. Samurai in Final Fantasy has been more abstract in implementation than even Dark Knight who has a lot of consistency between games. Samurai does not. Not within FF that is. And if you go for historical accuracy then as others have stated, they wouldn't even use their swords.
In Final Fantasy games, sometimes Samurai are heavy armored brawlers, sometimes they have a collection of supporting abilities, sometimes they're lightly armored quick attackers. In fact, the only thing they really have in common is the name samurai, and that they can equip weapons labeled as "Katana", but even then there's examples that stretch this, such as Auron who while his weapons are classified as Katana, they are almost all Broadswords or Greatswords in appearance. Dual wielding Katana are still using Katana and the argument for Samurai dual wielding is pretty much for the sole purpose to counter the argument of there being a supposed overlap with Dark Knight's Greatswords which is a pointless reason to not implement Samurai as potential Tanks.
If you'd actually read some of these discussions regarding Samurai, you'd know that Yoshi has said no such thing. Nothing as definitive as "Samurai will only be a DPS." Only that in his mind, because of the image he sees when he thinks about a samurai, lends itself more to a DPS (Since it's not the armor wearing variety of samurai). Every time he's mentioned Samurai and DPS together, there's been mention of it being a Tank as well.
There's nothing that says there ever has to be a sword wielding DPS job. No dev has ever said "We need a sword wielding DPS job." If they don't want sword users being DPS jobs it won't happen. There's nothing stating there has to be one. Besides, we know Red Mage is likely in the pipeline, you don't think that's not going to be a sword wielding DPS job? Every time people say "We need a sword wielding DPS" they seem to ignore that Red Mage is a very likely thing coming.