All the things you're saying regarding Killer choosing his weapons are not in the manga, mine are supported by panels and if what you say is true there would be really no logic.
Why should Zoro choose to use random halberds instead of
his swords? No reason in the world, especially in a critical situation
Why should Killer choose to use random scythes instead of
his blades? No reason in the world, especially in a critical situation
Is really that hard to understand?