What Dee did is no longer surprising. Death and destruction has been following him since the series began. He destroyed Nicholas's bookshop, Hekate's Shadowrealm, Ojai, Notre Dame, not to mention the Great Fire of London.
Dee didn't intend to loose Coatlicue on Earth. He intended to feed Josh Newman to Coatlicue and then he will loose her into Xibalba. Xibalba is connected to a number of Shadowrealms and by setting Coatlicue loose into Xibalba, Coatlicue will have access to dozens of Shadowrealms. Coatlicue will then destroy its inhabitants: the Elders that declared Dee an utlaga.