do you use 7 rogues in your city defense? Likely not - so why would you do that here...
If it's a PvP feature which it seems to be, and if they are to attack each other and not the computer like in GbG, both players have to be online at the same time in order for it to work.
If you're offline and have to assign a defending army for when the opponent attacks, no matter what units you choose, your defense bonus is gonna be less, a lot less than the opponent's attack bonus.
Let's assume there no bonuses, then 7 rogues with one strong unit which will be kept in the corner would be pretty destructive against an army controlled by the computer.
Let's assume both players are online, then 7 rogues would be their best choice unless they're noob or rogues are not allowed in the tournament, in which case none of them will send their rogues first because it's not the right move.
Even if somehow they make strategically right to attack first we will still have cases when both players skip their turn as long as they can.
Dont get me wrong, I love this new feature, I check the forums every morning to see if you have discovered new details, but I dont have much hope its gonna be flawless.