Where is that batrep located?
Thoughts:
Custodian: seems alright, 6+ isn't required. I would also advocate increasing the range to the tracking system, if anything, based on just the practicality of placing the models physically. It is for all intents and purposes a grand cruiser, but I guess the Tau could happily call it a battleship based on its weapons load out.
Protector: Agree with most comments, the T'olku does seem rather strong in battery strength. S16 equivalent isn't so bad though, it brings it brings it on par with the hitting power of a Carnage. I would feel more comfortable with a little less batteries, but I'll reserve judgment for more battle reports on how this fares. Agree with missile strength set to 5.
Emissary: The Sa'Cea is still problematic. You think that two gravhooks and two points of battery strength equals two lances? That seems a stretch to me. The grav hooks let you take wardens, sure, but it takes an extra 100 points to fill them out and not taking the wardens means they effectively give you nothing. The other two don't really have much difference. Missiles are better than the fighter, and that's makes the Bork'an a better choice.
Maybe give the Dal'yth the deflector standard since it seems much more defensive oriented, make the Bork'an pay for it, and drop the Sa'cea entirely?
Castallan is an interesting beast. Expensive, but man, that's some nice firepower and maneuverability. It's even LFR so it can hit pretty hard from abeam and fire those nice guided torpedoes. Should it really get 45cm batteries though for how small this guy is? Have Tau really advanced enough to get 45cm range on an escort chassis with few drawbacks? Should it have some limit to how many can be taken?