Oh ok I get it now xdWhy would the RP be nice to Samurai? They are the one who opted not to learn/use Ninjutsu xD
Anyway, you've missed a pretty critical point... look at the damage of the (Kusanagi no Tsurugi: Chidorigatana) - Grass Cutter Sword: One Thousand Birds Katana and look at the damage, specifically the note after it, of Chidori Nagashi. Then tell me what you'd rather use to hurt someone.
Chidori Nagashi when channelled through a sword gives only 10 Damage Points, assuming it is Freeform Kenjutsu while One Thousand Birds Katana does 40. So the former is more versatile while the latter is overall more stronger.