Savathûn could have been planning to attempt to use Quria to attack Oryx. When Oryx gifted Savathûn Quria, he may have made a terrible mistake. Quria, being a mind of the Vex, is able to summon them and give them orders. But now, Quria is placed under Savathûn's control, giving her basically two armies. She also asks Oryx if it will "let the machines into my throne..." in verse 44 of the Books of Sorrow, meaning she knows what Quria is capable of. By using her own brood, and the might of the Vex army, which kept the Deathsingers [u][b]and[/b][/u] Crota occupied for a long time. Combined with her forces, the Vex and Hive could topple Oryx and his forces. And then Savathûn will kill him, as this is the Hive way.