Copy-pasted from here for future reference when someone wonders how anyone could not like Fiona.
TL;DR without being a TL;DR thread.
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All these backstory contrivances are indeed eye-roll worthy exasperations, it's true, but they're not why I dislike her. The real reason is this-
Fiona is an awful leader for the mage rebellion she midwifed. She wants to be a rockstar revolutionary, but doesn't have the chops or the skills for it.
To start, she doesn't provide a goal or endstate to motivate or unify the mages behind her. Rather than set out a persuasive ambition and narrative that convinces a clear majority of the mages to agree with her viewpoints, the mage rebellion only kicks off because of a context that made many of those present fear imminent death if they did not declare resistance. From the start a critical mass of her movement was either uninterested or fixated on short-term survival, and not aligned with her vision.
Not only could she not define what the movement was for, but she could not unify movement either. Shortly after her leadership, the mages scatter and schism. I'm not doing her much of a favor by believing that she was uninvolved with the renegade mages in the Hinterlands. But that's just it- she was uninvolved, neither preventing or correcting the rise of a nakedly mage-supremacist movement in her own ranks. The Templar atrocities and crimes against the people in the area can at least be understood (but not pardoned) of the crimes of conducting a war and effecitvely a ruthless counter-insurgency campaign, but the mage conduct of setting little people aflame for funny looks doesn't even advance that argument. When one of the greatest political fears of Thedas is that mages outside of the Circles would seek mage supremacy and care only about themselves, Fiona's rebellion did just that. Instead of policing themselves to present themselves as noble revolutionaries deserving of sympathy, Fiona would not and could not reign in her movement to stick to an overarching strategy.
Some of this might have been mitigated had Fiona had some plan, had made preparations that might have enabled a mage victory regardless, but she didn't. She doesn't, and never had, the forces to militarily beat the Templars. She wasn't even intending to stage a rebellion for the purposes of subsequent negotiating leverage. Fiona's planning never seems to have extended beyond '**** the Divine,' '???', 'FREEDOM!' planning. There was no stronghold set up for a resistance if they were going to huddle up in a single place (bad idea), nor a pre-existing support network to hide the mages and smuggle them about if the intent was to avoid fighting (which she could have been working on for years). She's bitter that she has no allies... after helping evict a major nobleman of a sympathetic monarch who unnecessarily offers her sanctuary, and failing to set up deals or ties beforehand.
After being faced with the consequences of her poor planning that even a modestly aware revolutionary strategist should have seen coming, her poor decisionmaking continues with the Tevinter/Venitori alliance. Or so she likes to describe it as- an alliance is an arrangement against relative equals, and Fiona breaks a major Andrastian taboo (and political kryptonite to the hemoraphaging mage reputation) by selling her own people into slavery in the name of security.
Please, let that settle in a bit. The mage rebellion, a revolt against an oppressive security state that trades mage freedom for security, effectively ends itself by trading freedom (including, or rather especially, the freedom to own the consequences of their actions and choices) for the safety of servitude. Being a prisoner never forced to work but who could face illegal abuse or be killed unjustly? Unacceptable. Being a servant with even fewer legal rights, even less recourse to more infamous abuse, and likely forced to serve in the most active military of the world that views even your blood as a tool of value? Well, it's a dangerous world out there!
This is a deal so shortsighted that it's staggering. I, for one, am not inclined to blame the mages for selling themselves to the Venatori per-say. I still need a Templar playthrough to see if/when the mages knew what they were getting into, and if they stayed without magical coercion. But not knowing about the Venatori schemes is not a defense, because one of the big risks of mages is what they can inadverdantly get themselves into thanks to trickery (such as the demonic kind), and the Tevinter angle itself is sufficiently suspect that an ulterior motive should have been suspected from the start.
Fiona believes that Tevinter will protect her from the renegade Templar armies outside of her gate because... well, it's never clear exactly why she would think that. Because he said so, mostly. Did she really think the Templars forces who defy the Chantry and rampage in the borders of Ferelden will be cowed by the prospect of Tevinter reprisals? That the non-existent Tevinter army will stand between her and them? That uniquely Tevinter magic of a Magister and his retinue will do what dozens or hundreds of mages in the Hinterlands could not? If Redcliffe was going to fall to a Templar assault (an assault, it should be pointed out, that never came), then a Tevinter Magister's intervention is not a credible deterrent or defense. Not from defending against Templars, and certainly not from Ferelden's inevitable retaliation when the Arl is run out of his own castle. Tevinter not only would not fight a war with Ferelden for a city they have no supply lines to and no ability to keep, but they could not. The existence of an ulterior motive is obvious, even if not explicit, and the only obvious objective is the mages themselves. Alexius wants the mages, and wants them for reasons he does not think they would agree to if he told them, and Fiona sells them into servitude to him for a promise he could not keep if he was honest anyway.
There's more than a few parallels to the fears non-mages have about how Mages will inevitably resort to magical abuses or demons when desperate. Based on her willingness to throw away principles, break cultural taboos, and push down the surrounding mundanes in favor of the magi, it really does seem like the biggest reason Fiona didn't make deals with demons in Redcliffe was because an even worse devil in disguise approached her first. And considering that the 'disguise' part could just as well apply to the machinations of spirits... well, overall it's a utter failure of the argument that the mages could be trusted to not resort to desperate measures when desperate.
So, as a revolutionary, Fiona leaves a lot to be desired. She's not a rallying figure who leads by inspiring or convincing others to follow her. She's not a strong leader who can keep her subordinates in line and moving in a single direction. She's not a political visionary who could find common ground or strike bargains or alliances that people would be justified in having faith she would follow through with through thick and thin. She's not a competent military strategist who can recognize losing fights and adopt strategies that identify relative abilities and avoids being drawn into losing battles. She's not a careful conspirator who acts in advance, subtly crafting conditions to favor her efforts and ensure success before a confrontation even emerges. She's not a clever thinker who can identify tricks and traps and set her own while avoiding those laid out by those who would exploit and subvert her crusade for their own ends. She's not even a principled paragon who can inspire and gain ethical credibility by refusing to break her principles.
Any of those would at least be credible forms of a lead revolutionary. She is supposed to be an agent of independence and self-determination, but at every stage her ambitions rely on the acquiesence and protection of other, more powerfull people who could alter the rebellion's fate as they wished. First the Divine, then Ferelden, then Tevinter, and possibly the Inquisition, and then back to the Divine. All of these people had the ability to stop (and crush) her rebellion if they had wished, and the only reason she wasn't crushed was because they didn't want to (despite numerous deliberate offenses). Even in the most radically pro-mage independence playthrough none of the favorable results are a consequence of policies she has achieved or put into effect by influence or will, but rather a result of other people making policies for their own reasons. And if/when any of them refused to indulge her... she has no recourse, except to turn to yet another patron to do for her and her rebellion what she could not.
The fact that she's completely unapologetic about it? That she says she has no regrets and would do the same things again? That she doesn't even have the insight and humility to acknowledge her own shortcoming and failures and indicate an effort to improve herself accordingly?
Fiona isn't fit for what she tries to be. As a revolutionary, as a leader, as everything the mage movement needed to be a success rather than to just be. Instead she plays a major key role in getting a lot of good people killed for a cause she wasn't capable of carrying out on her own.
Can she succeed in getting her goals regardless? Sure- through no power or influence of her own. A recklessly reformist divine, a like-minded Inquisitor, a sympathetic monarch, a host of people who wanted similar things she wanted but couldn't get for herself. Even fools can succeed if other people gives them what they want.
Fiona isn't an idiot. She's incompetent.