It's kinda not though, since you fight outside on the citadel itself when you fight Halfus, and the rest takes place in the tower. Nothing about it is really connected to Grim Batol at all, and GB itself is just delegated to one dungeon. It's a very nice dungeon, but it's definitely not as worthy as a dedicated raid.
I'd even give it credit if Grim Batol were designed as expansive as Blackrock Depths.