Public approval is not a cumulative points system. The mages don't win ten points here, twenty there and, when they reach a hundred points, they are accepted.
Rather, it's something closer to this: mages help with a Blight or a war and, for a time, there is goodwill and they are granted concessions as reward. But, eventually, life moves on and people forget (much like what happens with the Grey Wardens). In the meantime, there are magical related incidents which raise tensions.
In Asunder, Wynne was nearly lynched in a bar and she had helped defeat the Bligth scarcely ten years ago. In Inquisition, all cities in Southern Thedas have closed their doors to the mages besides Redcliff and, eventually, they do too.
Off the top of my head, I recall three War Table missions where we have to rescue mages from normal people.
I think you're twisting my point. Of course it's not a cumulative point system but the Blights aren't forgotten. In fact they can be held up as great examples, during the time of the Inquisition, as to why mages deserve acceptance. 1000 years ago nobody would have ever thought that mages deserve acceptance, now by the age of Inquisition, thanks to things like the mage contribution to the Blights etc., people like Leliana do support the mages and can hold up these incidents as reasons for why mages should be accepted. How do you think people came to accept mages? It was because the mages have built a case through these events. Sure the Blights might not create any substantial change during the time, but it's always going to be part of history and it's always going to be an example that the mages can hold up and say "we deserve to be accepted". People look at that history, and the mages that they come into contact with, and think "why don't people accept mages? They've done so much to help". That's why this change has long been coming. And that is what Leliana is pushing for. Sure it's controversial. But the case is there.
One must take the mages' rejection in both Asunder and Inquisition as simple backlash after Anders and the Conclave. But by allowing the mages to help you draw a distinction between Tevinters, like Corypheus and the Venatori, and Southern mages like the rebels aiding the Inquisition.
As I said before, this did not happen overnight. It took a thousand years of good deeds by the mages to atone for the "sins" of the Ancient Tevinter Imperium and even then it's still a precarious and conflicted thing. The case, I can't stress this analogy enough, is there.
Edit: The other point that I think is fundamental here, but may have gotten lost in the wall of text, is the idea that mages now have sympathisers and supporters like Leliana and Mother Giselle. 1000 years ago when the Tevinter Imperium fell do you think anybody felt that way about mages? I doubt it. But by the time of Inquisition the good deeds of the mages have shown the world, that perhaps mages aren't that bad. So by this time there are actually people willing to push for mage acceptance aside from mages themselves. In that chaotic time after the Circles were formed I doubt anybody was willing to do so. 1000 years of change my friend.