I don’t have nearly as negative an opinion of Ikuko as you do, but I do agree that 8 (not 7) was indeed Tohya and Ikuko giving Ange their own advice on which way to come to terms with her grief and move on with her life.
To counter some of your points
The manga has an explanation for this, and prior to the manga’s release there was a different theory about why she knew the truth. Either way she does in fact know it.
[quote]These answers were gained by merging different fragments together and
removing Battler who knew everything. Will also played his part exactly
according to their expectations. If this isn’t a biased setting then
what is?[/quote]
I don’t really see any issues with this to be honest. When you already know the answer you can freely choose how to present it.
Did she really though? All the scenes of Ange in the human world, especially with Ikuko, as pretty suspect. I mean considering Ange had no memory of actually going to visit Ikuko, considering the events looped back several times to Ange on the roof, etc. Depending on interpretation it’s all part of the story Ikuko and Tohya are writing or it’s part of world (if you assume the meta world is not part of the story). Either way it’s certainly not the “real” human world.
I’d say there are two major points in favor of Ikuko. The first is that she refused to show the diary to the witch hunters. The second is that she (through Bern) was the one to bring Ange into the tale. I think it’s pretty clear that Bern and Featherine are playing the villain for a purpose, and aren’t really as evil as they seem. Bern guides Ange through the entire story, and though she often acts in antagonistic ways her actions are necessary. After all Ange is looking for someone to hate.
Tohya is the one that turned away Ange, not Ikuko. So Ikuko included messages for Ange in the tale, trying to guide her. Eventually Tohya realizes he should do something for Ange as well, and guides her in a different direction from Ikuko.
Featherine orders the destruction of the golden land and tries to take the catbox and make it into her plaything. However Ikuko does the opposite and brings together the witch hunters merely to scold them all for acting like goats. So why is she the leader of the goats in the catbox? Once again it seems like she is playing the villain, certainly she is preaching finding the truth to Ange, but her antagonistic nature is part of what leads Ange back to Battler, and towards an ending that very clearly indicates the Magic answer is the better one.
I think if you take everything about Featherine/Ikuko at face value then yes she comes off as a spiteful woman that doesn’t care about the heart of the tale. But I can’t see Tohya spending his life with such a person, nor did she seem that way in the final ??? when they met with Ange. Considering her contradictory actions in episode 8 I’m much more inclinded to see her as a figure similar to how Eva was portrayed at the end. Doing what she thought was best for Ange even if it made her seem like a terrible person.