From the look, Ninja will require physical stat such as STR, and then it will probably use INT for Ninjutsu. Usually, in any MMO, where you require to have more than one primary status, that class will have a huge disadvantage, so imo, it will not gonna be a pure dps type such as MNK, but gonna be a semi-support DPS similar to bard.
The main damage probably come from STR and their physical melee attack, whereas the spell gonna be debuff to the enemy, which make you not need to gain high INT to make them useful.
Either that or they gonna be a jack-of-all-trade physical/spell class that doesn't actually good at anything except look cool. (hope not)