Yeah but we know almost nothing about the Grey Council's part of the battle. I just skimmed through the battle chapter and we're told that Eb uses the Black Staff, that someone shouts "Fuego" (potentially a time traveling Harry), and that Odin/Vadderung helped open a Way. Even though there's a dozen figures, there's no description of anyone outside Eb and Odin/Vadderung that I was able to see. I suspect that the Gatekeeper is one of the 12 because Eb says something about traveling being easier with "a carpet to scuff your feet on" and, when Harry sees the Gatekeeper at the Outer Gates, he uses a flying carpet. We also know that the Gatekeeper was familiar with the Ways. That's still 9 figures that we know nothing about so there's plenty of room for Langtry.
I also kinda like the idea that Langtry is on the Grey Council. I could see him having a Snape-like arc in the end. It would go a long way to explain why people like Listens and Eb still support Langtry if they knew he secretly acts like Harry wants him to act while simultaneously keeping the White Council as neutral as possible. Langtry is also intelligent enough to keep his wards hidden from obvious view to give the White Council as much of a cover as possible.
