I know that this is old post and i know it is derailed for many pages =P But since this is in the strategy index and nobody has yet given this solution to the orginal question i still want to post it
So how to beat niefel giants whit EA acro? Short answer: chaff and reversed communion of mystics casting Gifts from heaven
The little longer answer is: In my opinion when playing acro (any age) you should be bying mystics from every castle exept capital. Mystics do 3 things... Research, forge and defend ur castles. About 60% of the mystics have atleast 1 earth magic and can be used for gifts communion.
Here is example of how to pull this off... Lets say u have 10 mystics, some oreiads and 2 turns to prepare... 6 of ur mystics have atleast 1 earth. We will use those. Forge 2 crystal matrixes. Put those on two lowest mystics on ur commander list. Script first four mystics to cast communion slave and then gifts (slaves will cast two gifts and pass out). Script fift mystic to cast power of spheres and then gifts. Script last mystic to summon earthpower, Gifts. Make oreaid cast wind guide to help giving those gifts to the giants. This will give u 14 guaranteed casts of Gifts each summoning 3 damage 150 meteors. Thats enough fun to smash 42 giants
More mystics = more fun
If you forget about that wind guide then this strategy is usable quite early in the game.. All you need is Thamaturgy 1 conjuration 3 evocation 5 and some mystics.