They where almost parodies of the typical archetype for "waifus" in anime. Asuka and Rei where meant to show how anyone with those types of personalities would also be pretty fucked up. Asuka, being the typical tsundere girl pushed to an extreme, had severe mood swings and would bully others because that was the one way she could feel like she is needed. That scene in EoE where Shinji jacks off onto her comatose body, that's meant for that to represent the fans who would buy body pillows and doujins of this fucked up and mentally broken girl. That's one of the main reasons Anno hates his fans, he made these characters to parody waifus, but the fans still ate them up without any sense of irony.

I feel like a lot of people missed the original point of this character