First, it's refering to a very specific and tangible thing, while none of the other titles do that.
Second, that tangible thing, depending on your point of view, is either (and most likely) the rebel base, or the Death star. Either way, it's a thing that, while certainly a part of the story, does not really embody the story. I think the titles should really Embody the overall story of the film. Balance of the force does that nicely, as the whole thing is very much about the balance of the force between good and evil. The Clone War again embodies the main thrust of the film. The empire strikes back completely embodies the story of the 5th film, and Return of the Jedi certainly embodies the 6th.
Thirdly, since it's taking the title directly from the film which inspired star wars, it almost seems like a rip off at that point. it's like "Star Wars is so much like the hidden fortress, we decided to call it the hidden fortress too!" I dunno, it just doesn't really do anything for me, I prefer A New Hope to the Hidden Fortress, at least it's original. After posting initially, "The Flame of Rebellion" really grew on me, I have no idea why, just felt right in my head. You of course must follow your own heart and artistic instincts, I just wanted to throw in my 2 cents.