That is just bad writing though? You have a mage that a dozen of veteran Wardens vouch and respect because of her abilities and determination. In DA:I she seems like a dumb milf. Sorry couldn't find a better word. There is literally nothing wrong with Fiona before that, many people accused her of being a mary sue, aka being perfect.
Which is the bad writing- the now or the before?
There's nothing unrealistic about a lucky leader who ambitiously goes for more than they can achieve and then fails. Or hubris to large to admit to personal failure. But Fiona's incompetence- particularly regarding the mage rebellion- was apparent even before DAI based on the books alone, when she repeatedly pressed for a revolution her people did not want and which she was not prepared to wage. That she relied more on luck than leadership was apparent in her backstory, and that she wasn't exactly big into creating solutions was apparent when she went '**** the Divine.'
What followed next, and the aftermath seen in Inquisition, was entirely predictable and in fact predicted: the rebellion failed for a lack of allies, a lack of preparation, a lack of experience, and would only be salvaged by the whims of others afterwards.
True, at the end he lost the control over Justice/Vengeance, but still not stupid. Did he know that he can not win there and in that minute, and also horrified, what he did. Ok, maybe he dont be martyr, but the process has started. Many mages freed. There will not be so, as it was before. That was his goal. No more. His long-term objectives (rather dreams) are larger. But as you wrote: he was not a conspirator or politics, or rational planner, just a poossessed, fixated, irrational (and crazy?) dreamer. (Still not stupid!)
The question is not was that he managed to free all of the mages, nor that this was right or not.
You're not being clear here. Are you agreeing that Anders failed to achieve his intended goals, or saying he did while talking smack about him at the same time? Right now the only thing you seem to be claiming was his goal was 'there will not be so, as it was before.' But Anders's position come Act 3 isn't to change the status quo for mage reforms.
By Anders' intentions, the only mages free after DAI are the ones who are dead or who haven't come back from hiding as apostates. Neither the Circles or the College were his desires, and the Circles and the Colleges both are in opposition to the hidden apostates.
The point, in any event, is that violent, murderous revolutionaries play JUST as much a role in bringing about positive changes to injustice as anyone else. Whether you like it or not, that's a fact of history. And one of the biggest ways they do it is exactly as did Anders: by giving reasonable people cause to step back and say "Hey, templars, you can't rise up and slaughter all the mages of every Circle in Thedas for the actions of one lone fanatic," which can quickly lead to "Hey, maybe part of the problem is that mages are being forced into desperate situations. We should rectify this."
This is not about the outcome itself, but enabling an outcome. Also it depends on how the character is viewed, Che Guevara was seen as a psychotic terrorist by the party he opposed. And he actually committed terrorism but he is a hero now. In fact chances are all our so called "war heroes" that exist in history of every single country and their epic struggle of independence were terrorist but because they won now they are war heroes.
None of this actually supports that Anders's efforts paid off to what he wanted. Anders didn't want a system of mage oversight and groupings they could live with- he didn't want any oversight at all.
I'm all for people taking advantage and validating terrorism, atrocity, incompetant bungling, and just plain luck... so long as they don't mind being judged by the same standard when their world is thrown into chaos by someone else with a pet priority. Also as long as they don't claim that fortunate fallouts of events that could have gone disastrously for the worse somehow imply competence and necessity for changes that they themselves frequently disrupt and prevent. For every 'violence was necessary for reformation', we can easily find even more cases where violence wasn't necessary, and didn't bring reform, making it merely banal increase of suffering.
And the comparison with Che isn't really apt. Che actually accomplished something he intended... and is mostly held as a hero by those who don't really care what his results actually were for the people who have to live with them. It certainly didn't stop the exploitation and oppression he nominally claimed to oppose, or protect the proletariat, or abolish disparity or bring prosperity and so on and so on.
The only scenario I see Anders being a hero is mages actually fighting all the none-mages then winning. In this scenario Anders could likely be called a hero/martyr depending on circumstance. Martyrs are people that die in backing their believes for the sake of backing them. In that sense Anders is a Martyr, since he is willing to commit a crime for which he will be punished with death, for his beliefs. So technically Anders is a martyr if he is dead.
'Technically,' martyrs have to be appreciated by the groups whose cause they stand for, or else they're just self-righteous dead people. The world is filled with self-righteous dead people, but being a martyr is a special sort of cultural context and appreciation.
The people of Thedas are the only ones whose opinion matters, and we've yet to see any significant appreciation for him from them. Not even from mages.