I don't exactly understand the point of the RNG.
RNG for the sake of RNG is just generally bad design I think.
And I say that as someone who enjoys the Chakra system on MNK ( currently, it used to be awful ).

What NIN needs imo is one more thing in the filler phase, 123 + Ninki spender is too little imo.
Personally I'd like to see Mutilate and/ or Dancing Edge come back in some form.
And also for Hide to actually be useful beyond just the opening.
I think that the ability in the Benchmark trailer that we saw NIN do might be the new Huiton and that it will deal damage and only be usable in combat.
I think they said that they wanted to fix the RDM awkward opener so they might want to do this with NIN too, and I think it'd be cool if they let us do hide in combat and that's how we do trick attack and Suiton does something else.
Suiton opening up for trick attack doesn't even make thematic sense imo.
And it kinda sucks that a sneaky Ninja doesn't use their stealth ability outside of reseting Mudras in the opener.