Nico Robin haki + rokushiki by xMrNothingx on DeviantArt

While Sanji was in Nami's body he used sky walk, does that mean

The Rokushiki Techniques Explained

Rokushiki, Wiki

Rokuogan, One Piece Wiki

One Piece: Strongest Abilities That Are Not Devil Fruit Or Haki

Busoshoku: Koka, One Piece Cruise Wiki

List of One Piece Haki Users

If there was a fighter with no devil fruit or haki, but they (somehow) mastered every fighting style. How strong would they be? : r/OnePiece

Rokushiki/Tekkai, One Piece Wiki

Why aren't there more characters who uses Rokushiki? Like if you spend your whole life being a swimming champion only to have to eat a Devil Fruit that throws away those years