Thief should be a subjob.

[Exstal]

Rogue is classified as a scoundrel - a damage based class. Thief employs trickery, a trickster in itself and a mugger of treasures, also a damage based class as well.

The problem is this; Naoki Yoshida (FFXIV's director) wanted to call Rogue, "Thief". However, the lore team said that that wouldn't fly because having a guild of thieves inside of a city state wouldn't make sense. Could you imagine down the street from your house are a bunch of blatant criminals who teach you that you should be robbing other people? So because of this line of thinking Thief was renamed to Rogue.

It also has Thief from FFXI's most known moves in it, as well as the iconic skill, "Mug". So unless they decide they want to add Thief as a secondary job to Rogue, we can just assume that Rogue is Thief and that's the end of the train of thought for the people currently working at SE. You don't have to like it but as per my sig, I perfectly understand why it'd be pointless (check that link if you want the full story).