The deck have some potential but it's hard to trigger the slowing power cause you rely on conditions and you need to have at least 2 or 3 southrons passin alive to regroup, so against a solid fellowship you will have a few chances to do so, in my oppinion.
Maybe
Company of haradrim with the boat engine plus some bows and some other minions that could pass to regroup without many problem. But i like the first idea, maybe we can work on it to see if we can improve it even more!