filecopy function is slower than cp command

When copying a 7 GB file, the filecopy function is always about 20% slower than the cp command. I tested using my MacBook Pro 14" M1 and an external SSD connected via USB.

• Mac to Mac

  • filecopy: 4.78s
  • cp: 3.40s

• Mac to SSD

  • filecopy: 20.22s
  • cp: 15.93s

• SSD to Mac

  • filecopy: 20.61s
  • cp: 16.64s

I use the following code:

let openPanel = NSOpenPanel()
openPanel.runModal()
let source = openPanel.urls[0]
openPanel.canChooseDirectories = true
openPanel.canChooseFiles = false
openPanel.runModal()
let destination = openPanel.urls[0].appendingPathComponent(source.lastPathComponent)

source.withUnsafeFileSystemRepresentation { sourcePath in
    destination.withUnsafeFileSystemRepresentation { destinationPath in
        let state = copyfile_state_alloc()
        defer {
            copyfile_state_free(state)
        }
        let date = Date()
        if copyfile(sourcePath, destinationPath, state, copyfile_flags_t(COPYFILE_ALL | COPYFILE_NOFOLLOW | COPYFILE_EXCL)) != 0 {
            print(NSError(domain: NSPOSIXErrorDomain, code: Int(errno)))
        }
        print(-date.timeIntervalSinceNow)
    }
}

and the very basic cp command:

time cp /path/to/source /path/to/destination

Is there a faster way to copy files? Am I doing something wrong with filecopy?