Originally Posted by
GloatingSwine
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They had absolute confidence in their ability to deal with Wanda Maximoff. They had completely failed to understand the scope of the problem...
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Since there was a powered Wanda in their universe, they most likely assumed that that was the power level they would be facing, i.e. pre-WandaVision boost, and Darkhold to boot. In any case, in-universe explanations for how they were defeated so swiftly are easy to find. Thematically, it played a little like Oberyn being defeated by the Mountain.