right now I feel like the war of faction is just based on the time when you play amd not on the skills of the players.
I am unsure of this could be fix or that Ubisoft will actually take the time to change that as it is not really broken but anyways... my solution would be to give add an asset multiplier.
The way it would work is like this: if their are 4000 players online(2000 vikings, 1500, knights, 500 samurais), divide the total number of players by the number of players in each faction. so vikings 4000/2000 = 2, knights 4000/1500 = 2.6, samurais 4000/500 = 8. that number would be the multiplier number.
So when playing a game your assets are distributed depending on how well you played and then multiplied by the multiplier number. That even if you are almost alone in your faction at the time of your game you still feel like your efforts make a difference.