I didn't think much of Sisters, until I saw the White Dwarf codex. I would buy an Sisters army now if I had the money, as the new mechanics impressed me, seeming both fun and effective.
As a very very avid Sister of Battle player, I have to say that fluff wise: the sisters have almost no business traveling to a different planet with a force as large as 2000pts would grant, unless it were a special request by the inquisition. The reason I say this, is that they are content to send squads and a maybe a small contingent out, but a whole army? That would leave a shrine and reliquaries unguarded. The only thing that I think could get them to do that is a special request (whether they listen is a different matter). Even the force that went to repopulate/retake sanctuary 101 was around 1000pts (in game mechanics-wise).
I love the sisters, but no fluff I have ever read would ever justify the army traveling around, unless it by inquisitorial request... or even possibly special astartes request.
This is why I think having an inquisitor (albiet I don't think an ordo mallius inquisitor is appropriate... they have other resources and channels) and the inquisitor's resources in a Sister book is accurate. Do I think they should domineer the book? Absolutely not. Should they be an option. Very much yes.
I guess it's a sign of the times that it's no longer one of their FAQ's to ask "When will Squats be back."
But it seems that when it was written that way back in 2nd ed when they were released (and throughout 3rd/4th with the Witchhunters codex) sisters were mainly pitches as "allies" for IG/SM, rather than standalone armies. The fluff fit the marketing strategy. I'm happy for the fluff to change in that regard.
The new fluff in the WD book helps with that, it hints at the possibility of their being far, far more SoB then the original books imply, plenty for their to be expeditionary forces as well garrison forces in shrines and such. When there were only 12000 odd SoB in the Imperium it didn't really work so well.
Ask not the EldarGal a question, for she will give you three answers, all of which are puns and terrifying to know. Back off man, I'm a feminist. Ia! Ia! Gloppal Snode!
Didn't the original fluff specify "countless minor orders"? or am I starting to go senile?
However the process of robo-insemination is far too complex for the human mind!
A knee high fence, my one weakness
Sisters have always had their Wars of Faith which they have every business going into. They are more than a defensive force. In fact the way their rules are constructed they do poorly if they mainly defensive IMO.