I don't understand it either, from may last game for example:
Enemy Ships Destroyed: 109
Personal Ships Destroyed: 8
Most Powerful Ship: Tranquillia Fleet 36
Enemy Soldiers Killed: 4 Billion
SCORE: 767
The one who got the highest had:
Enemy Ships Destroyed: 0
Personal Ships Destroyed: 0
Most Powerful Ship: Mining Starbase 20
Enemy Soldiers Killed: 0 Million
SCORE: 1314
I lost maybe 4 ships total, the only thing i can think of is that he had a higher rating the first 3/4th of the game, while i had very high near the end, is the score only based on the average of the military rating per turn? It seems a bit strange to me that you can be the best in military without firing a shot ever...