Also, yeah they could be Adepta Sororitas soldiers, but not full Sisters of Battle, and then I complain even less. Most of the soldiers who fight for the Eccliesiarchy, just as for the Departmento Munitorum, would have "lesser" arms and armor, rather than Space Marine-like power armor and boltguns.
Actually, there's no such thing. All Adepta Sororitas soldiers are Sisters of Battle. Other members of the Adepta Sororitas do maybe help with a war effort to a degree (notably, I'd expect the Orders Hospitaller to be there, patching their sisters up).
There are no other soldiers fighting for the Ecclesiarchy, due to the Decree Passive. There is the loose rag-tag Frateris Militia, but they aren't actually soldiers for the Ecclesiarchy and don't belong to any kind of command structure, they're just plebs and peasants out with pitchforks.
The Adeptus Ministorum (the Ecclesiarchy) are specifically prohibited from keeping any men under arms. Which is why they have women under arms. Because in the Grim Darkness of the 41st Millennium, the spirit of the law is poppycock, the Lex Imperialis is mountainous, and the Ecclesiarchy has good lawyers.
And those of the Adepta Sororitas that are soldiers belong to the Orders Militant are the Sisters of Battle. The only argument I could see is the one they actually present in Dark Heresy, where the lesser-equipped members of the Sisters of Battle (that you are assumed to play, as far as I remember) are Initiates, barely fit from deployment, and then you get swooped up into the Inquisition.
I WOULD complain if the Battle Sisters (maybe not every Adepta Sororitas) didn't have some Faith ability; that's what makes them cool, to me, and shows that the Emperor is still doing something individual people can see.
But.. he's not. That's just it. The God-Emperor has no way to grant wishes and prayers from half galaxy away. His fading powers are used to direct the Astronomican and keep the door behind the Imperial Throne firmly shut, lest daemons come pouring in.
From a strict observers objective viewpoint, the Emperor absolutely do not grant miracles. Now, some people within the universe thinks he does, and their faith are so strong in the God-Emperor that their combined efforts sometimes results in clear manifestations of the warp. What the Sisters of Battle and the Adepta Sororitas practice is pretty much mass hysteria and unwilling witchery.
[...]Sure, he's fighting the Ruinous Powers, and keeping them from eating Humanity, but they fight each other plenty, too, and may just be waiting for a 14th Black Crusade. He lights the Astronomicon, and helps keep the psyker pop under control by eating them, but many people never leave their world, or see the Emperor's light (I have a Navigator who is strangely religious toward the Emperor, though not the Ecclesiarchy, so much, because she actually KNOWS He's there, as she is guided by His light; a really fun littl bit of that story), so it doesn't always FEEL important, but Acts of Faith show that He is still there, even if that's BS, and the Sisters are actually just using latent power; while people who need proof of miracles can be said to in truth not believe in them, I argue that, sometimes, a little incidental proof doesn't hurt.
As for DH's Faith at Will, no, I don't really care for that, either, but I do like my Priests and ASors to have SOMETHING that says "I am more than just a simpleton with a weapon; what I am saying is TRUE!" Might not hurt to whip up a Faith trait, ala Pure Faith, but like Psyker (X), or Untouchable (X), and assign some more limited powers to them, like Ork psykers do, and MAYBE make each cost a Destiny point, like last-ed Star Wars Saga did with Force Secrets. A little less availability, and a little less surety, but the power to make the unnatural happen, because the power is there.
Except.. it's not. It's why I really dislike the Dark Heresy Faith Powers. Pulling off feats of strength, fervor and fanaticism is, on a personal level, by the individual sororitas or priests, perfectly fine. It makes sense.
That a single priest or sororitas would be able to pull out a Faith power on command is nothing short of straight-up psykerdom or sorcery. And what's worse, the truly learned of the Imperium would know this to be true, to one degree or another.
Now, it would be really cool to play a Sororitas that actually is a psyker, that genuinely believes that the powers she uses is straight-up from the God-Emperor himself. Hell, unless she's in bad luck, she might even become a Saint because of it, pulling off faith-healing and burning the wicked, left and right.
But more likely, they're recognize her as a psyker and off to the League of Blackships she'd go, because the Sisters in the fluff absolutely hates that kind of stuff, and I'd be surprised if the Sororitas didn't screen for that on initiation. The Schola Progenium does, and as I understand it, a lot of the Sororitas recruits come straight from there.