Kidd's fruit could have been one of the coolest of the manga, surely one with a lot of possibilities, and instead got only the most bacisc, and tbh lame, usage.
The sword would have been great but yeah, better using some metal scraps lol.
Truth to be told, this should be a teaching moment: 99 out of 100 times Oda just puts things there becuase he likes them. He doesn't think at all about them or has any plan about them. We saw a giant sword seemingly out of place and though "what a hint, surely he wants to use it in some way". In fact, probably Oda just tought "we are in the samurai saga; why don't I put a random giant sword in the Island of the villain ?! Soo cool".
He probably has never had any idea at all about actually using It.
Then there si that one time out of 100 in which he actually put there something to be used after.