Maybe it's the bots? As they use past history, the more the line-ups win, the more that they use that same line-up. A bit of a self-fulfilling prophecy.

On a large mana battle I would like to see if my Yodin Zaku line-up beats the Death Summoner line up. Some large ranged attacks and explosions to nearby enemies from Ettin Spearman, Pyromaniac, Fire Demon, and Mantoid will cause a lot of havoc. Should take care of the Death Elemental and Skeleton Asassin within a round or two.