Harry's had enough exposure to Faith magic that I think he would've noticed if any of the Senior Councillors present in Turn Coat's island battle were Saints.
Langtry, in VERY scary circumstances in the same book, also didn't seem to need faith magic, just excellent normal magic.
In Proven Guilty, Michael's presence provided power that the present Senior Councillors could not (and Michael is all Faith).
So to me, Gatekeeper is the obvious option, and would neatly answer the question "why are the Angels not providing any help at the Outer Gates?" (answer: they actually are, in the most effective manner they know, by empowering a mortal).