The only thing Ninjutsu needs is a way to punish delayed wake up. It negates the pro of having f2 to counter wake ups, but since we lack mix-ups and respectable pressure, the most we'll get is a throw because they'll just block low until they see us lift our leg up. Even you stuttered your b3 or sparingly used f4, with f4 being pretty react-able, it diminishes the probability for an opening, so more times than not, we won't get any damage off are knockdowns.
(d4 is good) f2, b4, and b2 are great for whiff punishing, but they're not good neutral tools. They don't space out the opponent, the don't stop the opponent from coming in, they're just good on the opponent's recovery. If blocked or whiffed, the opponent is in and maybe have punished you. Since they're not overhead/lows, they're going to be blocked a lot and since they're not fast, you can't use them near the opponent because you can get out-prioritize. I'm not saying these moves are terrible or even that they need a buff. These are just the facts that lead me to believe that it is highly unlikely for a ninjutsu player to win off the neutral alone, meaning that damage on the knockdowns would benefit us.
So I think we should get a variation specific f4 (maybe with out flames to show it's different), that can be held to become unblockable the charge would be meant to catch long delayed wake up, this would give opponent a window to attack on their short delay, meaning they'll have a reason to hit buttons on their wake up. This would give us 3 ways to open up the opponent for combo, f2 for armored wake up, frame trap for short delay, and f4 for long delay.
I would really like to debate this proposed change with someone to see how viable it is or to make it viable.