King's sword is no different than Kata's Mogura. He uses it in conjunction with his devil fruit ability but is not his main fighting style, when he fought Luffy he used it minimally then when push came to shove he relied on his mochi and future sight. We haven't seen much of what King can do so we are in the early stages of seeing how strong he truly is, similar to Katakuri but for some reason people forget that. The point is King chose to confront an Emperor and her crew without his sword that is all, you can try to twist it but that's what he did, a swordsman does not jump into battle without his sword no matter what the fight may be.
