Don't you have that backwards?
No I believe I have it exactly correct.
321bar pointed out the basic reasons why, but there are a few more subtle, yet very important reasons why this would be good for the game.
The two peak arenas will be up for 9 hours, as opposed to the offpeak arena which will be up for 15 hours. Creating a goal oriented game environment is critically important for the survival of this game! Players must believe they can accomplish what they wish to do. If that is win the war, then they must have the chance to do it. The only way they can do that is on a smaller map right now. Basically each country has one week to win the war before the titanic tuesday reset. On peak hours, each arena will have 9*7=63 hours of battle to win the war. Off peak arena will have 15*7=105 hours of battle to win the war. Just going off this math, the off peak arena should be more difficult to reset.
Do not take this point lightly. Win the war players are extremely important to the health of this game, and if they feel they can win, the game will be much better for everybody.