GrudgeBringer, I assume you have some type of bless for your sacreds and are having trouble getting enough of them together. It might be worth recruiting some Nemedian Warriors. They are very similar to Tir's troops and should do fine against infantry. The Fir Bolg Warriors you can recruit are also not bad and have a low resource cost. Mixing them (they have good defense) in with your larger units will prevent your giants from being swarmed.
I've never played Fomoria but I'm familiar with Tir na n'Og's units and Fomoria has many similar troops so I thought I'd suggest it. Hope it's somewhat helpful; I'd be sorry to see you go AI, mortal enemy of the Tuatha or not.
