If everybody would know that you can quit a battle at any time and still receive your hard earned damage done, this discussion wouldn't even be here. Am I right?
Well, it all comes down to spread this information, in game, to make it clear for everyone.
A basic idea would be to give all players in a match a pop-up when every active (non disconnected) enemy vessel has sunk.
<Message Box>
All active enemy vessels have been sunk, you can now leave the match without any penalty.
1. Quit match, return to the match result screen.
2. Stay for more free xp
Just as an idea.