Fire Control Groups
The Issue
Managing large engagements can take a lot of clicking to handle target assignment. The existing tools to copy targets between ships are all based on doing so to ships of the exact same class, which can mean that doing something as simple as concentrating fire on a single target requires assigning the target many times. And splitting fire between ships can mean falling back on manually assigning targets to every ship (and fighter...) in the fleet. Then you kill your targets, and have to rinse and repeat. Assign Sub Fleet can help a lot, but isn't flexible, and obviously depends on everything being the exact same class.
Suggestion
Fire Control Groups. Every fire control can be part of an unlimited number of groups. These groups can be assigned targets, which get assigned to every fire control in that group within range (with the Range x2 tickbox allowing shorter range weapons, or nearby ships, to also be assigned - maybe adding an x10 or bigger as well).
This could then be used by the player in many ways. I'd set up some permanent groups like All Main Guns, or Everything Including Gauss. These would be used by any fleet to quickly concentrate fire from multiple ship classes. In an established fleet, I'd also set up some groups specific to that fleet - splitting the fire 2 ways, and 3 ways and 4 ways etc. Letting me easily divide my fire based on the targets I was facing. Or it could be used just to combine certain types of ships that I think of as being the same, but are separate classes in game terms due to minor changes.