He won't be saving it, if he wants to make an AC army. If he saves it, the army will take 5 turns longer to fill. I am not trying to argue one way or another, as I would not be sure how I would go, until I was actually playing.
A 2 unit AC army could do some damage, till it got the 3rd unit. The only problem wiht a short army with a units of 2 defense is once damaged, they can be killed. It all comes down to what the situation looks like. Again I could go either way, I just wanted to point out some of the options.