would giving ninja provoke /ja be game breaking. i dont think so. heck give it to PLD while your at it. would make for some crazy awesome tank action.
I'm not convinced that it would change anything. I mean, it would be a very good off the cuff enmity spike but so far as subjobs go I don't see anything changing.
NIN doesn't sub war in merits for voke, they do it for berserk and DA, both are borderline broken on NIN because of how they relate to dual wield and katanas.
NIN doesn't sub war for tanking because our damage is lol on endgame mobs, /drk facilitates all the hate we will ever want for.
PLD would still sub /nin for anything that matters, because shadows are that good. They already have several ways to produce hate, natively. Voke being added to their arsenal would only make the wedge between the utility of NIN vs. PLD that much greater.
What I mean to say is if tomorrow SE added provoke to both NIN and PLD's JA that it wouldn't change what we sub, it's not that important to have provoke in todays FFXI. It would be nice, much nicer for PLD I'd venture, but I don't see it as being a necessity.