Had British and French gunnery already diverged?

Had the Royal Navy and French Navy already developed distinct approaches to shooting by 1759?

Not really. Their gunnery practice was still developing, and specialized gunnery officers were only beginning to appear.

The later contrast in national shooting methods was not yet fully established in 1759. Both navies were still developing their practice, and specialized gunnery officers were only beginning to enter service. Quiberon Bay therefore predates the more mature systems of naval gunnery associated with later periods.