If it is a totally randomized/quick match battle maybe the matching system could look at players kill/death ratio and automatically assign players to get the teams as close to as possible. Also maybe some multiplier for the different types of ships to help make it "fair".
I.E. Team 1 - 2 players, 1.5k/d, in frigates, will says has a level of 2, so 1.5(2) + 2(2) = 7
Team 2 - 4 players, 0.75k/d, in sloops, say level of 1, 4(0.75) + 4(1) = 7
If something kinda like this system was used you might be able to have some fair fight while making it interesting.