Not true. The term "haki" was first used by Blackbeard during Jaya, chapter 234.
Mantra is definitely CoO which was introduced in Skypea arc, around chapter 250+
Remember that Smoker, a logia, was introduced at the very early stages of the story and Oda probably had some sort of blueprint for CoA so Luffy could fight logias.
He used "willpower" if I'm not wrong, which is Haki translation.
Ofc Mantra is CoO, why are you saying it like it's not confirmed lmao?
Anyway, that's irrelevant like I said. If Oda finally wouldnt have decided to implement Haki, Mantra could have stayed as Mantra and that's it.
On the other hand, Mantra is irrelevant in this topic about swordsmen and Haki, which obviously centers about Armament and AdCoC, which are the Haki that enhances the output power of an attack.
Like I said, it's irrelevant the "hints" until chapter 500+ or so, when Haki is introduced explicitly.
Until that point, Zoro was a swordsman and that's it. Therefore your thread does not make any sense trying to join both things when they could live apart perfectly fine.
So no, Haki does not make a swordsman.
You can claim that it was a hype moment that got retconned to CoC, but there is no way to prove it. Canonically, Shanks used CoC against the lord of the coast.
It's a fact that it was retconned to Haki.