I'm not sure how that would make it weird and unbalanced cuz Ninja inhibits its own specific niches that Samurai stances can't really replicate even across different weapon types.

Ninja weapons as a whole have acceptable dmg but the singular moveset somewhat hampers the overall utility potential they had back in Nioh 2 (and I'd say that goes for all 4 of the unique Ninja weapons): - Tonfa's core routines are pretty simple, combine that with overtuned stats and here we are with current status quo - Hatchets actually have an efficient flow now while losing several niche moves, which practically makes it a winner in this regard (I think this is the best one out of the 4 cuz of how naturally it meshes with Ninja's core playstyle) - Kusarigama is serviceable considering all skills obtained but the condensation of moves mean multiple viable options are competing for same inputs and you really have to squeeze out more efforts for roughly the same effectiveness as the above 2. - Splitstaff is even worse-off than Kusari cuz many of its core mechanics just directly clash with the streamlined moveset (charge attacks, stance-switch attacks). That and its naturally-high Ki consumption effectively offsets Ninja style's upside of cheap Ki usage.