The power of those 1-shot WS's has less to do with the number of hits and more to do with their pDiff bonus's. SAM's Y/G/K has a relatively low fTP but the 2.0 attack cRatio multiplier makes it almost always cap attack. Even if they give NIN's a 75% STR 1 hit (2 with off hand) WS, the low D on main hand weapon combined with no pDiff bonus would make it kinda suck. The need to introduce a good 4~5 hit WS that doesn't have crap modifiers (Ku).
Then the problem there, is multi-hitters crit or not need high amounts off attack to hit for decent numbers - you know if your not getting those attack buffs at most it'll be a Jin+1.
I can't really see NIN havin a good ws the way SE makes them atm because of their low dmg rating like you said and only way to get around that is to have large ftp for a 1Hitter or sexy WSC mods for a multi-hitter.
Maybe give NIN Sneak Attack?
Beyond joyeuse/ridill WAR's, and hardcore ripped Axe/joy war's, it kinda was. On merit level stuff, and at least before the 2H update.
They wern't though really, we only pared Ridil war's and 25% haste BB Mnk's with the U/U combo with 40% DW before the change to the TP floor.