That isnt a cap problem thats horde sqauds that like to attack undefended bases. The side with less personal has less watching for NOE raids 
Its not about attacking undefended bases or NOE tactics.
What I'm getting at is for some reason because of the caps, there is a mass exodus of a country in one arena, while that same country will have the #s in the other. The country in both arenas that have the lesser of the other 2 now have the other countries trying to wipe them off the map, while the other fronts have almost nothing going on.
What I have seen with the one big arena is that you ll still get the NOEs, you will still get the hordes. You hardly see any front getting dominated. I think this is because if there are larger, more even #s on all sides, it evens things up and even if there is a horde somewhere, you will tend to get more support if you are on the receiving end of the horde.
I don't know why this happens, but it does. Personally I was much happier without the caps