NIN CAN be good at other stuff, NIN/RNG using Guns with high marksmanship can lvl NIN up to around Yhoator and no more than lvl 30-ish without tanking. NIN/BLM with all elemental staves and ALOT OF GIL can use ninjutsu to attack. However NIN/BLM is far from practical, while NIN/RNG up to around 30-ish is somewhat acceptable except for the high cost in ammo and skill up.

Eh i cant find the post i did on this on my LS forum but NIN/WAR tanking with full evasion gear is more typical and more effective of a NIN. Before NIN was known to tank, NIN were gimp and were not used for anything(not invited). But with tanking availible you can easily be invited now. NIN would be a good DD with shurikens but the high cost of them and the factor of no Throwing WS makes it a waste to use most of the time(esepcially without capped Throwing, throwing away shurikens and missing will cost you dearly).