[Agema]

That will give you a vastly destructive force of giants - for a few turns each battle.

Your first problem: You only get one giant per square and giants are very expensive, so your army is small and doesn't hit many opponents. Each turn, with two attacks, each giant will probably kill 2 opponents, but take 8 fatigue. Step forward 13 turns, and your giants collapse unconscious from exhaustion. So you can only kill (giants x 2 x 13) enemies before you slow down a lot. It's very easy, particularly against undead or spells like swarm, to meet that many enemies, and your cold aura isn't going to help you that much.

Here you meet your second problem. Giants have a ton of HP, but they will steadily take damage, and they'll take a lot more when exhausted. Thus your 70-HP giants are actually starting to look very vulnerable and very easily to kill after a few rounds of combat. If your opponent has spells like Stellar Cascades and ohters that cause fatigue damage, it's going to be even worse. Although without regeneration from a nature bless, they merely need to throw enough of any damage spell and your giants will die eventually.

If you are going to bless giants like that, the optimum is always going to be taking high Earth and Nature blesses. Earth prevents them tiring out, nature allows them to take vast amounts of punishment. E9N4+ is what you want to look at.