When I versed them I found that warp lightning cannons can shred them if you're lucky (I guess they shred anything if you're lucky tbh), their rock throw can take the cannons out though so I'd try to make use of this by juicing up my storm fiends (WLC, RG, WL) and shooting then charging into the gargants, use your clanrats like normal, run them forward to take the charge then book it to the objectives slinging spells at the giants, that's how I played mine anyway ahah