just a reminder at all the people saying thief must be a jobs and can't be the class, in Final Fantasy (the first one) Thief is the starting jobs and when you make it evolve you get... Ninja ^^.

other point i highly doubt that we will get a tank from the scout class, mostly because it's an heresy any good tank will tell you is not good and will often be either underpowered or overpowered.

in the cut scene we can notice two thing about the two fighting style:
- Yugiri seems to be more Area Oriented and attack multiple target and have some sort of control.
- Thancred is more about attack one target at the time.

this is the difference we can see:
- ninja is about DD AoE with CC a bit like the mage.
- Thief is about mono target probably with some debuff/support.

and you get two different jobs that will fit in two different role. (even if they are both DD)