If Osiris has been, corrupted, possessed, compelled by mind magic or some Supreme leverage.
By Savathun.
I would find it out of character if Saint-14 didn't declare war on the Hive.
My ideal Witch Queen trailer is Saint-14 slowly walking into Old Chicago feeding shells into [b]Perfect Paradox[/b].
...
It would also seem a little "dismissive" if Saint-14 didn't try and move heaven and earth for Osiris; he's done it before by going into the Infinite Forest.
It's also what any straight man, with Saint's personality, training,gear, and legal authority would do.