Defend creates problems ... everyone knows that
I'll explain further shall I?
It's a Command that must be given, which, when everyone is under haste with a high SPD stat, means that you need to do it repeatidly while idly waiting for Omega to perform his Terra Break.
That means there is a chance of Omega getting in his move before you can instruct all three characters to repeatidly go into Defend mode.
Furthermore, it means that you can't have a player in Beserk mode, which saves a lot of time in a no Limit-Break game.