Queer Cosette, You're Such A Lonely Child

Pansexual and genderqueer white student, unresolved pronouns (she/her and they/them if you gotta!) with an interest in tea and knitting. Current fandoms: Marvel Comics, Les Miserables, Welcome to Night Vale. Operating on Eastern Standard Time.

You have a fair point, but given the fact that Ystin calls zirself ‘Sir’, refers to zirself as a man on several occasions in the series, I think it would have been simple enough to use male pronouns rather than misgendering Ystin altogether.
Venditti seems to be under the misapprehension that this run of Demon Knights is Grant Morrison’s Seven Soldiers, where Ystin was literally a girl in disguise. That’s clearly not the case in Demon Knights, which shows a disrespect for the character and the previous writers.