Hitech was looking at an idea Luschu suggested that looked promising, but until then, YES it is necessary. The timing for when the arenas split are due to the time the the US starts signing on. If they do it earlier it would take longer to populate each arena enough to bump the other arena. If they do it later, the first arena population would be so high that it would take a long time before the population in the low numbered arena could start opening space in the closed arena.
The time they have it now populates the arenas quickest and more evenly.