@Grisznak  
to be fair that was not a pyker. that was a pretty powerful deamon. at least with cain.

@Kazapsky  
What if they went against orks?

@Macharius
 
Sly Marbo is a major character and thus has plot armor and the Rule of Cool to hide behind. Strip him of those protections and he will get annihilated by the first xenos he runs into.
 
As for the Sororitas, you’re not helping their case any by pointing out they need help to get things done. If they’re teamed up with the Guard, it will be the crushing numbers of the Emperor’s Hammer that get the job done - the Sisters are simply too few in number, and too weak individually, to carry a major battle. If it’s the Inquisition they’re working with, they and anyone else along for the ride are disposable filler for the Inquisitor in question. Bring the Marines into the equation and the Sisters become even more redundant.
 
Functionally, the SoB are stuck with the worst of both worlds - they’re human, but they don’t have the mindboggling quantity of reserves of the Imperial Guard. They have power armor and bolters, but both are flatly inferior to the Space Marine gear they imitate: a Sister is slower, weaker, more fragile, and her gun is a much smaller caliber. And their vehicular support is basically nonexistent - they have no main battle tank (the Immolator is a joke of a substitute), and little else besides basic transports.
 
The Adepta Sororitas could be a solid faction, if GW would just put a little work in. But as it stands, they’re underpowered, understaffed, and underequipped for the battlefields of the 40k universe. Alien invasion? There’s not one major Xenos race in the fluff the Sisters stand any chance against if it’s more than a small task force. Chaos? Even more lopsided. Minor uprising? The PDF can usually handle that, they have the numbers to cover the ground better, and they’ll cause a fraction of the collateral damage.

@Kazapsky  
That’s like saying that Sly Marbo is human and therefore hopelessly outclassed by everything. Apart from the fact that he’s basically the single most deadly human in the entirety of the setting, including Space Marines in that count.
 
Also, Sisters generally aren’t thrown against opposition as stiff as the Space Marines are expected to go against - mostly it seems to be cultists or a smattering of xenos. From what I’ve seen they don’t into battle alone as well, unlike the Marines. Usually they have a force of not-quite-Guardsmen or, in serious cases, Inquisitorial Stormtroopers backing them up.
 
Of course, their equipment is actually very, very good. Their power armour, while not as advanced or quite as durable as Astartes armour, is still one of the toughest things around. Their mainstay weapon is actually the boltgun, despite the fact that they are usually depicted as being holy pyromaniacs. Of course, Battle Sisters are still a few cuts below Space Marines - but remember that Space Marines are a couple of dozen cuts above most things in the setting!

@Grisznak
 
Part of the problem may be that most of those scenarios are actually plausible.
 
The Sisters of Battle operate on a heavily simplified version of Space Marines doctrine - relying on a small number of fighters in power armour to plow through any opposition.
 
Problem is, the Space Marines are superhuman even without their fancy suits, and are much better trained, and more heavily armed. In short, they can get away with such brazen tactics. The Sisters, for all their spouting off about faith and whatnot, are still fundamentally human and thus hopelessly outclassed by everyone they could conceivably go up against - except the human servants of Chaos, who tend to hopelessly outnumber them instead.
 
The fact that their preferred weaponry puts them within spitting distance of said superior opposition simply makes it worse.

@Macharius
 
As i stated it’s a article from 1d4chan. Its exaggerated. As far as I remember Sisters of Battle in a “Duty Calls” helped in stealing Shadowlight which could awaken latent Psyker and boost power of active ones. It was only a squad or at best mission. I don’t know about the rest of situations getting them thoroughly owned.

@Grisznak  
‘Another whole Order Mind Controlled by one chaos Psyker. Why, Sandy, why?’
 
Which book was that? I don’t remember reading it in any of his Ciaphas Cain novels.

@Kazapsky  
Space Marine Guideline 1: Thou shalt not refer to the Adepta Sororitas as “Bolter Bitches,” nor shalt thou go anywhere near our sisters during the time of their “Red Rage,” lest thou wishes to be the first human to enter orbit without the aid of a shuttle.
 
Jokes aside. Sorry for its longness
 
Article from 1d4chan, part about them getting thoroughly owned.
 
A whole Order turned to Chaos by one Slaaneshi Keeper of Secrets.
 
A whole Order Mind Controlled by one chaos Psyker. Fucking Goto.
 
Another whole Order Mind Controlled by one chaos Psyker. Why, Sandy, why?
 
A strike force of Celestians and an Inquisitor being killed, cannibalized, and sacrificed by the Sons of Malice Astartes chapter for disturbing their victory rites and falsely accusing the chapter of heresy. (Imperium does nothing… Apart from declaring the Sons of Malice to be heretics anyway.)
 
A whole Commandery being killed by Flesh Tearers Astartes chapter (who were eating allied militia at the time). (Imperium does nothing.)
 
Three whole Orders killed by the Space Wolves Astartes chapter when they try to inquire about that ship full of unarmed priests the Space Wolves shot down earlier. (Imperium, again, does nothing.)
 
99% of sisters in the galaxy vanishing due to to a retcon in the two whole paragraphs of fluff given them by the 5e rulebook.  
Considered by most to be proof of what was to come, considering the clown-car that is the current Sisters of Battle army on tabletop.
 
A whole shrine-world of Sisters killed by Chaos Dreadnought. Said dread shrugs off meltas, meltabombs and multiple Exorcist volleys, a Living Saint even gives up her divinity to stop it, and fails. It’s destroyed instantly when a Marine throws a hammer at it. We are not making this shit up.- +Hell Brute, not a dreadnought+
 
An entire Order of Sisters of the Order of the Sacred Rose dying and ultimately destroying their base and everyone in it, who were sent to the Kaurava Campaign and killed by Vance Motherfucking Stubbs after they refused to fuck off. Unlike the majority of the entries on this list, the Sisters led a valiant defense action, crippling the Imperial Guard forces for weeks and hamstringing the Imperium’s campaign to reclaim the worlds of the Kaurava system. Also, unlike the others on this list, the Sisters were the aggressors. So this doesn’t really count as much.
 
An entire convent of Sisters killed by Grey Knights, their bodies violated and their blood applied to the Grey Knights’ armor, so the Grey Knights can be immune to demonic corruption, even though they were already immune to all forms of demonic corruption, due to the fact that they are the Imperium’s daemon killers. See also: Khornate Knights.
 
Necron Phaeron Trazyn the Infinite keeps the head of Sebastian Thor mounted on his wall like a Deer Trophy. God damn it, Ward.

@Grisznak
 
Come to think of it, Ward’s not the only guilty party here. The Sororitas seem to be the go-to target for the Worf Effect in 40k.
 
I mean honestly, does anyone write fluff for the Sisters of Battle that doesn’t involve them getting thoroughly owned?

@Kazapsky  
Matt “Spiritual Liege” Ward.

@Xhydralisk
 
And anything else written by Matt Ward.

Just stay away from Ultramarines and Grey Knights…

GO TO THE KITCHEN BOLTER BITCH

@Macharius  
Yes, but Golden doesn’t realize he’s dressed an adepta sororita and not an adeptus astartes.

I didn’t know the Pretty Marines were accepting ponies.

@Background Pony  
‘his Primarch’
 
U wot m8? It’s clearly a Battle Sister, not a Space Marine.

Well, Commissar Cain was right about one thing… Tech Priests are, in fact, capable of having a sense of humor. Also: Quick, someone tell him that his Primarch is Rawbutt Girlyman.