Wrong, if you queue for Seal Rock, you won't get in. It seems as though the roulette heavily favours Shatter, meaning it is impossible without a premade group filling most if not all of the viable slots for the Seal Rock instance. This means that the main motivation for doing it, ie the Field Commander achievement reward, is not actually possible to obtain in the game's current form.

All I ask is that the achievement for this set of glamour be changed to incorporate ALL frontline instances, or at least more than JUST Seal Rock, because otherwise you have a piece of content with an impossible barrier in front of it, and that's never a good thing.
Alternatively, please make the outfit obtainable through other means. I mean hell, even Savage gear is obtainable without doing Savage. It just happens to be only dyeable through Savage.