You're using that argument to protect a story that began with a girl and a woman being the only two to die on screen, the woman being fed to the male lead, and then the male lead going on a masculine and manly adventure to save the poor helpless womens. And then you went and claimed that this was unavoidable because the majority of the Nasuverse cast is female.
So no, I don't think that argument is valid here. At all.
Yes, actually, it is
entirely valid here. In fact, it proves my damn point entirely. Just because the two people shown to die are a young child who happens to be female and a woman who is the least powerful of all the adult characters around that does
not make it sexist. You could genderflip all of the characters and I don't see any reason to believe Lantz would have written the story any differently.
And, well, yes, if the majority of the cast is female you'd expect the majority of the people dying to be female too, that makes logical sense. Particularly when the only men around are ones who can fight back more effectively than just about anyone else. And, Lantz has explained his reasons for doing it that way, reasons which have bugger all to do with gender, either explicitly or implicitly. Shirou couldn't be shown dying because he would have fought back more effectively (due to UBW) and that would have given Toshi time to get everyone else out. And Archer was just plain not there, because it's not his house.
I'm not saying the scene in question was perfectly written, but it was
not sexist. Just because a woman dies it does not make the damn story sexist, and nor does having a male lead make it sexist. Half of the damn population is male, it is not shocking that stories have male leads.
I'm not saying such sexism does not exist, at all, but you cannot say "oh, Lantz uses a male lead who goes off on an adventure to save
everyone (which, yes, includes Shirou, who I believe did die off-screen) therefore Lantz is sexist". If we were to follow your logic then all main heroes would have to be female and all characters who got killed off for plot reasons would have to be male.
Basically, you know someone's there but you just don't give a shit about him. It's how Obsfucate works. It isn't invisibility as much as the vampire making himself simply not noticeable. He's there, but you really don't care he is, or even really noticed. For that matter, I doubt that any of your characters would be able to notice him because it isn't a violent action, isn't drawing attention to himself, and isn't hostile. He's just there. Obsfucate isn't invisibility, but it's close enough for most purposes.
Plus, Sashimi and his cult haven't dealt with Kindred before. They've got nothing to work with regarding Jack.
I would expect a bunch of magi, heroic spirits etc. to be more resistant than most to such mental manipulation, though. Not being violent helps, yes, but I just think you should have given us the chance to argue it first.