I am not a Ninja by any stretch of the imagination but i have one in my lowman Abyssea group which consists of six people.
From what i can tell you, Yurin: Ichi is actually very good for NM's with devastating TP attacks. It's slight but you can notice the fewer WS's from the target and when you're fighting something like Minax Bugard and Flame Skimmer which have pretty unpleasant WS's.
I've noticed that TP feed on Abyssea NM is more of a problem than the NM itself usually is, so much that i've had to have DD's stay back from the mob at regular intervals when doing a run with my LS. I think Yurin and Myoshu were designed with lowman NM fighting in mind. I still have one of our members of the lowman group come Ninja pretty much all the time.
I would not write these spells off, they have a use, just not one most people would notice at first glance.
Beyond this place of wrath and tears
Looms but the Horror of the shade,
And yet the menace of the years
Finds, and shall find, me unafraid.
It matters not how strait the gate,
How charged with punishments the scroll.
I am the master of my fate:
I am the captain of my soul.
Invictus -- William Ernest Henley