Maybe not so much underestimated as that is honestly the best chance we have. Agree that stegs are a bad idea, though impact hits will get a bunch of them down those WL are still striking first all the time and as ZaGreekie said will eat stegs. Thats a very expensive unit for HE and I'd say more powerful against LM than a lot of armies since we don't have much in the way of ranged shooting to bring it down. Soften up as much as possible with skink poison shots, and try to get a salamander or two to hit it (they have a pretty big potential range if you roll well with artillery dice) but then best bet is to try to redirect it and keep it away from combat. The spells will fly everywhere but a large unit of WL and 2 characters is a huge point sink so point denial is probably the best bet if you can't reduce it enough at range. Also remember the WL will deal a large amount of damage, but when we hit back they will die quickly so keep deep ranked units to fight them.