Briala is much better than her at the Game.
Briala was hardly a player. More like Celene's piece. Her goal was to improve lifes of city elves, and she helped Celene having that in mind.
But it was Celene who was able to see past her affection, burning the Alienage to the ground - sure, it was Gaspard's trap, but avoiding that would end in losing the support of important nobles - much worse in long-term strategy than possible assassination. That was a good decision from the perspective of the Grand Game. Sacrificing her servants, yet saving Briala's loyalty was a genious move that secured the throne for her AND gained her a loyal spy and assassin.
Briala was nothing but a piece in Celene's machinations, which she realized at the end. After returning to Val Royeaux, elven situation would not change. Celene would not free them from alienage, cause that would be more trouble (nobles) than actual profit (elven army). Most likely some elves would be elevated to level of assassins or spies using Eluvians, but that would be it. Unfortunately for Celene, Briala realized that. It was hardly Celene's mistake however, she did what she could.
There may have been real affection on Celene part, but she was Empress. The Grand Game, the throne and the country must always come first for someone of her position.
I think that this is what causes Orlesian Empire to be the most powerful nation, and what causes Farelden to be a much weaker state. The quality of the ruling class.
Nobles in Orlais must learn to play the Game, where personal affections, feelings and commitments must often be sacrificed for power, political alliances and influence. Both Gaspard and Celene are capable rulers, who know a lot about ruling country and swaying nobility. On Farelden side, we had:
Maric - did not even want to rule, was ready to sacrifice himself, while his only son was just a child, leaving freshly reclaimed country without leadership.
Cailan - a big child with dreams of honor and glory, with his wife ruling the country behind his back.
Loghain - would be quite good if not for his paranoia about Orlais, which unfortunately overshadowed real goals and threats.
Anora - probably the only capable one.
Alistair - hardened is not that bad, and may prove to be a capable ruler in time, unhardened is just a whiny brat who doesn't want a throne.
None of those rulers actually have any experience in politics, apart from Anora and to some degree Loghain. Hell, Alistair even admits that he prefers to follow than to lead! I'm sensing another occupation of Farelden quite soon. Political class of Orlais is leagues above that of Farelden.