Tevinter also nationalized their entire Chantry so that was kind of inevitable. Tevinter is also a mageocracy.
Is that a good thing? Most people don't think so.
To start, Orlais needed to not court a Civil War. It needed a noble class that, if not actively behind the monarchy, was at least ambivalent to the Throne's programs or powerless to oppose them.
Has this ever been enforceable in Orlais' style of government? Is this something you can put on Celene, or the insubordinate nobles? Or both...
Celene knew Gaspard was against her, and she knew he was gathering support. Her closest adviser, and in my opinion the real reason for her successes, spelled out the best possible method for dealing with the opposition, and Celene was too selfish to take it. She put herself before the nation. It's not even ambiguous when she does it.
How do we know that marriage was the best option, though? Gaspard's and Celene's differing strengths and weaknesses seem to compliment each other on paper, but they tend to disagree on, well, almost every policy. It seems easier for the sake of convenience but I don't really think it's conclusive as far as strengthening Orlais, especially if its rulers are constantly in a state of struggle and conflict.
Now, effectively disarming Gaspard by marrying someone else of great status like Remache but limiting their control of the throne, on the other hand...