The Balrog defeated the dwarves of Moria who had better weapons and superior organisation, culture, technology, you name it ... Why would the orcs of moria fare better in a fight against the Balrog? I don't think that they would stand a chance. Considering how primitive orcs on their own are (and the Orc population of moria seems pretty autonomous) they probably have (after a few hundred years in Moria) developed their own religion around the Balrog and worship him as a god while he is barely aware of them ...
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