I didn't say anything about stability, I just mentioned she roflestomps Fiona in my ending. It mentions the mages that were in the inquisition. It didn't mention her specifically, but until they do later, she's dead as dirt for me. Especially on my templar playthrough.
It also doesn't imply anything of the sort. It says she's met with resistance, which she stomps out quickly, and that her reign could end shortly or last long, and it could go either way depending on if the chantry chooses to stand by her. Do I think it'll last? Hell no, none of them will if you ask me. But the ending does not say what you wish it did.
She stomps the mage resistance, not the people. Also there are two versions of her. If she disapproves she will fail as a divine and you will get these on epilogue:
"In the end she is victorious, but not without much bitterness and loss of life."
"Even so, this new Divine's reign is troubled, and signs of fracturing within the Chantry grow daily. Many believe its days are numbered."
if she approves you get:
"Some say it is only her warm relationship with the Inquisition that ensures her victory."
"For now, the Chantry remains united. Though difficult for many to accept, a mage sits on the Sunburst Throne and will remain there."
Where as Leliana is completely successful in either case. She either charms everyone into her way or threaten/blackmail/kill them. Unity is mainted if you make Leiliana divine regardless of anything. According to what happens at epilogue, Leliana is the only one who removes all resistances and restores long lasting unity.