Yup that’s what I dislike in this interaction.
Necro Sienna seem more like something they wanted to do mechanically and had to find a way to make it work rather than the other way around.
Like OE, SotT and WP were clear narrative evolutions, more so for Bardin and Saltz, but Kerillian make sense with it, wood elves, protective of the weaves, those are things that are at the basis for the Sisters (Honestly the only 1 I can dislike is the Handmaiden).
As for Grail Knight, it’s a different case. The End Time make it that the Lady (Remember that GK are a scam to get protectors) has to scramble and get any person that is worthy of it.