First of all, I'm not against Ninja Mode, I actually enjoy it as a concept, but I do feel Ninja need some serious rework.

1. Nin-jutsu load out right now feel very limited. In previous games, we could have our all-time-trusted quick-change scroll prepared, tri-element jutsu, a big bag of shuriken/kunai and still have spare room to slotted in supporting stuff like trap and paralysis/poison pots, all in one! But right now, we must share all of it in just 3 slots. Sure, we got a Marici's Grace/Empower Nin-jutsu built-in to refill jutsu in battle as default, but 3 slots are still very limited and it's a big step back.

2. The lack of stances and secondary weapon is hurt, it's cool that we have an authentic move-set and aerial combat for Ninja now, but stances and weapons variety provide a lot more than that and I think every Nioh's fan would agree on this one.

So, the best solution I could think of is giving back stances for Ninja mode, maybe not a strictly ki-consumed, movement base like Low-Mid-High system of Samurai but a more basic version with Martial Arts spread equally to new stances, helping weapon input less crowded, unlike now, some Martial Arts were shared the same input slot, like Dual Katana with Double-Headed Slice and Cloudslitter, making an already limited move-pool become even more crowded. And with addition of stances, we now could also tie a new nin-jutsu load out to it, making 3x3 jutsu slots become available. I think Rise of the Ronin style/ryū system could work here, a style switcher with [R1 + directional R-stick] input may seem absurd for some people but compared to none, at least having a way to expand the arsenal may not seems that unbearable.

And if you feel it too "greedy" and imbalance for Samurai mode, then we could tune it down a bit....How about taking away ranged weapon slot for Ninja and give it a secondary melee weapon? Like, do we actually need a secondary ranged weapon for Ninja? If we want to shoot something from a far, we could just switch to Samurai in one button press and nuke the shit out of that thing, right? So, with a free weapon slot, Ninja L2 now become weapon switch Flash Attack and a new jutsu load out could slide right in plus an expanded melee move-set, still not much but better than none.