"They"? Not the writers, at least not K.A. One or two of the ghostwriters didn't get Rachel, and the fanbase took that train of thought and started pulling characterization out of their asses. Like #48. Sure, there is a book with Rachel as a power-hungry psycho, but it was ghost-written, during a period of sucky ghostwritten books, and Rachel in that book doesn't mesh at all with the Rachel of the established K.A.-written books. So, pretty much, it's not a good example of Rachel.
Look at Rachel in say 1-20. Look at Rachel in her final scenes in 53/54. That's not a bloodthirsty Viking killer chick, that's a decent & wholesome average suburban kid with a pretty significant assertive streak to her personality. Sure, she's sarcastic, sure, she's not tolerant of a lot of BS. But this "Rachel was at risk of turning into a crazy warrior woman with no empathyyy!" is sooo dumb. She never straddled that line at all.