I'm a bit torn on this. On one hand, there definitely seems to be an issue where some of the ideas and design choices in the manga are ... not great. You brought up the use of indigenous aesthetics for "savage, bad giants", but there was also the line in chapter 11 where she says "Those who hold no beliefs, have no dogma or creed to follow, are in capable of treating other people as human beings!" which is incredibly similar to lines used by some religious groups to demonize atheists and agnostics in the real world.
I read that more as Hinako saying “If you have no personal philosophies or moral standards that you hold yourself to, you can’t possibly treat other people with basic human respect.” She even states before that line that she’s not talking about any specific religion or anything. She’s saying that if you don’t have ethics or a conscience, then there’s nothing stopping you from doing horrible awful things to people and treating them like trash.
Atheists are more than capable of realizing that it’s immoral to murder people. They don’t need a religion to tell them that. Hinako recognizes this. Her wording is probably kinda confusing since she mentions “having a God”, but we’ve also seen her define “God” as less of an established, definitive deity and more like some nebulous force of the universe. So I don’t think we’re supposed to be taking Hinako’s words as some sort of Christian crusade there. Just her saying “if you have no sense of right and wrong, you cannot possibly treat people right”.