I don't think I'll ever understand the logic whereby finally getting resolution on a storyline that the books have been developing since 2003 (Andorian reproductive crisis), and making use of a plot device that the novels have had since 2005 (Taurus Meta-Genome), after directly building upon work established in a previous book from 2011 (Paths of Disharmony), constitutes a deus ex machina. A deus ex machina would be if the Q had cured the Andorians five pages before the novel's end after all of Bashir's efforts had failed. It involves the sudden intervention of exterior agents who have had no prior involvement in the storyline and whose solution is one the primary characters have not worked towards or earned themselves. The solution to the Andorian reproductive crisis was the culmination of years of foreshadowing, characters' efforts, and the use of a long-established plot device. You could reasonably call the Taurus Meta-Genome a McGuffin, but it is not a deus ex machina.