Sorry, but you people don't know what you're talking about. Your concerns are understandable, but mistaken.
Separate arenas DO work; they worked for more than 10 years in AirWarrior. Just because AH hasn't used separate arenas yet (the poorly-implemented CT doesn't count), doesn't mean it can't work. Remember, there were flightsims around long before AH!
The key to making separate arenas work, is to cater their size to your nightly player base. In other words if you have roughly 400 people on per night, create two arenas limited to 250 people. At first some people will complain, but in whithin a month it balances out and you'll wonder how you ever got by before.
Also, a good idea is to give the alternate arenas slightly different "themes"--for example, AirWarrior used "European" and "Pacific" arenas with somewhat different planesets. Not only did this add variety to the game, but it also made Japanese and USN aircraft more useful since they didn't have to compete with often superior European equipment.
Another good idea for AH would be to have one arena like the current setup, and a second arena as a 2-sided Western-European planeset arena with a RPS in place. Haven't a lot of people been asking for just such a setup?
Again, I stress--just because it hasn't been done in AH before, doesn't mean it CAN'T be done. Separate arenas CAN and WILL work.
J_A_B