Eviscerator - the canoness kit includes one. It's not as chunky as the repentia one, but the kit includes a double-bladed, hand-and-half chainsword, if I remember.
Combi-weapon. This is more of a throw-in, but there is a sister superior model which blatantly has a combi-unspecified. (it's actually an old auxiliary grenade launcher, I think).
Plus, if you want a flying canoness, you can take celestine, even if you don't call her that.
I personally would not bother shooting a landraider with retributors as you can only glance, and a single glance will take slightly more than 2 turns shooting.
I wouldn't for preference shoot at a land raider unless I had no other target. That wasn't what I was suggesting. But the point of retributors is that with
divine guidance, they can now hurt anything, meaning there is always something worth shooting at with them. They can kill anything from hordes to monsters to heavy infanty up to and including medium tanks pretty reliably, and in extremis can hurt a land raider from outside meltagun range.
Also, an exorcist also takes a couple of turns fire to glance a landraider; average 3.5 shots, 2.3 hits, 0.4 glances. Granted, it's an AP1 glancing hit, but it's still only glancing and the exorcist isn't half as flexible when it comes to stuff like crowd control.
Yes, faith is a bit rubbish. I use it in the following order: rally fleeing sisters (quite common now), retributors, dominions, battle sisters shooting so it rarely gets past the dominion stage. By the end of the game, I may have virtually nothing worth spending faith on.
Rallying fleeing sisters is no more common than it was; stubborn never helped against morale checks from gunfire, and a unit breaking and running from combat with only I3 is generally caught and killed. Light of the emperor isn't that good but as noted it's the bottom of the priority pile to be used. Faith is nasty, just accept that you can only reliably use your veterans; acts of faith, and the novices only get it occasionally, as opposed to the army getting more faith points than bolter clips, which kind of spoils the whole 'miraculous' thing.
I'd agree you may not be able to spend 6 points of faith towards the end of the game but I'd be surprised if there's genuinely nothing to spend any on. Of course, you mentioned that you use Jacobus and a conclave for close quarters, and he both increases your expected faith pool
and doesn't drawn on it himself.