My only objection is it would honestly make the guns OP. Lumberjack and hades are already very powerful if the shooter gets the beat on a ship in that first or second shot. Being able to spam their first volley would honestly break balance imo. It sucks as it is going against the top tier gunners and even they usually miss their first shot.
If it still needs to be nerfed I'm open to ideas, but I currently don't think so. I see the current idea as balancing it's own use on two main aspects:
1. Tunnel Vision:
Keep in mind that just to use the range-finder is already sacrificing a pilot slot and tying up one crew member to its use. If it's given to an engineer, that's someone who isn't repairing or shooting, and if it's the pilot, that's someone who has sacrificed some of his maneuverability (one less pilot tool remember), and is zoomed in on one single ship, and focusing on relaying instructions, meaning he's paying less attention to the battle around him outside that ship. This alone means that with one person drawing fire it would make a teammate more potentially able to sneak up on them. I realize it doesn't guarantee it mind you, but it's a lot more to have to focus on while zoomed into a single ship and concentrating on adjusting a gunner's firing arcs. I may have to try flying with spyglass constantly zoomed in to test this. Potentially, we could even require a ship to be zoomed in on a certain amount, for example, make them take up 75% (arbitrary number, this could change) of the range-finder's view for the arcs to appear. This could also help facilitate communication between captains as well, since being zoomed in means the other pilot would have to warn you of incoming ships.
2. Delayed Reaction:
When you tell someone to do something (repair the engines, or open fire for instance) they're not going to immediately parse what you say and respond. Even the best players will still have a little delay, due to the time it takes for the server to relay the words coming through your mic to their speakers, and simple human reaction time. The delay between telling someone information and the gunner responding and correcting means it's not necessarily an immediate and surgical hit. You'll have to have some REALLY good communication skills to catch the faster ships like the squid, or even a medium speed ship that suddenly uses hydro, to the point where it would probably just be more reliable to let the gunner try aiming on their own because their reaction will be faster and you have to focus on maneuvering the ship to keep up. At this point the squid, in this instance, has closed inside your arming time and is killing you, and you're down a pilot tool because you brought the rangefinder. This leaves you even more vulnerable than sniping ships at close range usually are, and more reliant on your teammate, because you probably need him to bail you out.
Another smaller difficulty is the way the current shot indicators interact with clouds. The moment that line hits a cloud it stops right then and there, which would of course make using it for long distance sniping hard, and give opponents the chance to neutralize the rangefinder's effects by using clouds for cover.
I see where you're coming from. More lumber and hades hits = bad time. That's a valid concern, and that's the main reason why I nerfed my original idea into where it is now.