Originally it was theorised that because we had no 1 - 1 scale maps we needed the 2x multiplier to balance things. However with the option for bigger maps that is no longer valid, and hasn't been for a long time.
Part of it is balance, without the 2x multiplier the short ranged fighters would have a distinct advantage. You'd see 3 x as many la's and yaks as you do now.
Part of it is the way the arena is setup, and that won't change as long as we have a open main arena where you don't have to fly 200 - 600 miles to attack the enemy.
As much simulation as AH is, in many respects it can never duplicate the Battle of Briton. Your simply not going to be able to have 109's over dover knowing they have 5 - 10 minutes to mix it up then they HAVE to rtb or they are going to be ditching in the channel.
Myself I think the time has come for a new arena. One that is built to scale, with historic distances, with no spitfires fighting spitfires. The problem with that is that people always want to be on the winning side, so which ever side has the advantage, always ends up outnumbering the other side. Which I suppose leads us to why HTC is trying to develop the CT concept.