She has successfully ruled Orlais...for years until she let her country go to ****, enough for Gaspard and other nobles to become disillusioned with the empress's rule and believes it's time for a new leader to make Orlais strong again. Celene...the long term planner leader? This is the same woman who supposedly a shrewd politician, very skilled at the Game, yet she fails constantly in TME. This is the same woman who couldn't think of other ways to send a message to Orlesian nobility without risking herself, so she march to Halamshiral to quell the elven uprising without a second thought, only to be walked into Gaspard's trap and almost lose her life.
Let's face it, Celene is not the flawless leader like you made out to be, and were it not for her weakness and incompetence Gaspard and his compatriots wouldn't doubt the empress's rule and rebel in the first place.
I never said she is flawless, but she is basically a better ruler than Gaspard could hope to be in every way. Gaspard didn't rebell because Celene was ruining the country. Orlais has never been quite so peaceful or prosperous as it is now. He rebelled because he wanted power for himself...and as your advisors point out, many chevaliers followed him because Celene tried to improve relations with Ferelden/Nevarra. They saw her as "antimilitary". But that doesn't make her weak or incompetent. As for Halamshiral, even Briala said that Celene had no real choice in the matter.
Isn't it implied Briala was mostly responsible for her successes in the first place?
She certainly played a big role in Celene's success. That's why I reconciled them in the game.