Why does Izou use guns?

Guns are mechanical and bullets have a fixed speed, obviously depending on their shape and the power of the gun. Point being you can’t train to make your gun better. Since One Piece characters move at Mach F**k are guns just worthless weapons?

Why would a Yonko captain use them as a primary weapon? Does Haki increase bullet speed? Are One Piece characters slower than we think?

As an aside how does Izou use these like smgs? Is that an anime only thing, or is it like Isshin from Sekiro?

Guns are mechanical and bullets have a fixed speed, obviously depending on their shape and the power of the gun. Point being you can’t train to make your gun better. Since One Piece characters move at Mach F**k are guns just worthless weapons?

Why would a Yonko captain use them as a primary weapon? Does Haki increase bullet speed? Are One Piece characters slower than we think?

As an aside how does Izou use these like smgs? Is that an anime only thing, or is it like Isshin from Sekiro?