[thejeff]

You have heavy protection troops, but even their protection isn't enough to protect them from the giants strength, and their high resource cost prevents you from massing them.

Try mixing in lots of low resource independent troops to swarm the giants. Preferably low protection high damage troops, barbarians maybe? Anything but your heaviest will die in one hit anyway, so protection doesn't really help. Go for numbers and damage. Swarming will drop their defense so you can hit them more.

Your heavy crossbows on "fire large monsters" will help a lot.

I wouldn't bother with Legions of Steel, unless you can target your guardians. Strength of Giants might help though. Not sure what research level that is. Destruction is good. Maybe Blade Wind, though it'll slaughter the crap troops I'm suggesting.

Longer term, any smiths that got the fire random can do Flaming Arrows.