Rather than all style, they seem to mean it as at the bare basic form, all stance originate from this simple stance, face your enemy, ready to strike, ready to counter.Sword god using all the sword styles. Seems appropriate.
similar to history strongest kenichi and baki, just when it's getting good with a mix of different backgrounds and styles, author pull the "but nihongo martial arts are superior" trope.This mandatory nationalist propaganda arc kinda less interesting than Sasaki Kojiro tbh
No culture clash, just straight up oooo japan ooooooh aaaaaahhh