Is targeting topmen similar in principle to destroying a gunnery spotting position?
Short answerBroadly, yes: both attack the personnel needed to keep an important shipboard function working.
NotesThe comparison concerns disabling people who make a ship's fighting systems work. At Cape Finisterre, canister aimed into the rigging threatened the topmen needed to handle sails and preserve maneuverability. The reply accepts the broad analogy with attacking a gunnery spotting position, whose crew helps direct a ship's fire.