The answer to the question if restated, "What would make players want to balance the fights?"
I dont think the "average" player ever ups to balance a fight. He/she will up to win a fight or some how gain from the fight that is joined. It could be as you say that some extra motivation could be providd thru score although I cannot see the mechanism other than a local ENY which is transfered to all aspects of score. Which is not of import to all players.
From my perspective the inability to launch and gain any alt over a horded base just means I move to another base but some times this is too far or too much time or too porked to make my reprisal worth while or in any way rewarding. I suppose horde busting via 262 is plausible its just not the game play I enjoy.
So fix No.1 for me would be to remove the hordes target from the environs of my air field such that I could up to defend the skies over local (no more then a sector away) towns or vehicle fields. My air field would be heavily defended by auto AA, Puffy AA etc etc. If you want to kill my airfield then it should be as heavily defended as any Cv group and more.
If you want to capture my air field then you better move the front line a bit closer by capturing these towns that are just a sector away. But I want to be always be able to up to defend from a field within a sector of your target. Further if you capture I want to be in a positon to immediately re capture if your not organised enough to hold it for a given period of time.
In this way we do not assume to control the horde. It will still overwhelm its targets (but the air field is not one of them so it will not deny us access to local game play) So we neutralise its ability to deny us access to local combat
by capping our fields. Then we exploit its greatest weakness........ its not organised. It has to hold the the town or GV field it has just taken......auto AA has not popped up magically and now it has to defend......... both sides have access to the field of combat.