Since everyone put their
"reasonable" analysis of why Luffy
"can't shouldn't" use swords, then let me also put my opinion using the similar logic on this thread....
First, lets start with this statement of Luffy
"I can't use a sword! I can't navigate either! I can't cook! I can't tell lies!"
"What can you do then?"
"I can beat you!"
So from this point we knew that it was Luffy's job to beat
"main/strongest boss" of every arc.....
Now, things got changed in Wano.....as things stand, Zoro is going to participate and wound Kaido because he
"got enma and cover page/Ryuma" foreshadow....see at best there are two or three foreshadowing is enough to say that Zoro goes against Kaido and
"sharing" Luffy's job...
Now why can't Luffy use swords as there are enough
"heavily" implied hints present here and there like
1) Luffy used sword in thriller bark
2) Luffy posed with swords in two or three cover pages especially with one or two of them with cursed sword Nidai Kitetsu
3) Luffy carried sword with him in the whole act
4) Luffy was trained by swordsman of Roger Pirates
5) WB uses blade weapon/Luffy's inspiration Shanks uses sword/Roger used swords and since Luffy is going to become PK and inheriting the will of Roger he also can inherit swordsmanship as a part of fighting style exactly like him as Zoro inherited Enma.
6) Luffy has just learnt
adCoA/Ryou which is also called
BOAT/GOAT/VOAT(Luffy already has this) and is a swordsman technique and Grandpa Hyo is a swordsman he could have taught Luffy a thing or two about using swords.
7) Lastly,
"I will cut Kaido down" statement is uncharacteristic of Luffy as he always says
"I am gonna beat you down/I will kick your ass" can be considered as
"nail in the coffin" that Luffy incorporates swordsman ship in his fighting style.
From the above seven
"heavily" implied hints, it is not far-fetched to conclude that Luffy incorporating swordsmanship into his fighting style is
more likely than or as likely as Zoro wounding Kaido
it just makes him more versatile and as @Monkey D Theories said Brook's role is musician but his fighting style is swordsmanship....
But worry not, just like how Luffy is the one finishes his job, Zoro is the one who is going to be strongest swordsman and WSS while Luffy is going to be PK.
PS: As for other things like being cook/doctor/navigator/shipwright/musician...it was never
"hinted" at any part throughout the manga and once Luffy cooked food and it was
"gag" so it was not considered.