Re:Madoka Potential: The idea of all of her potential being personified as Sabrina is an interesting one but doesn't seem to logically follow from the mechanics we know, but that's not enough to go on. Still, we should be able to ask Kyubey.
Re:Madoka wish ideas: Fuck you guys I still say if we let her do so at all she should have Hope control to complement our powerset. We'll have THE BEST fusion attacks gtfo.
re:Witchbomb and excuses. "Oh shit Mami muh brain damage. I have these memories and some of them have been wrong and some haven't and I didn't want to say something so horribly devastating without having absolute certainty. I could test the lichbomb thing but witchbomb? No real ethical way to do so. Anyway list of apologies."
Wishes are generally not monkey's paws. You get the intent of the wish.
It wouldn't really be a monkey's paw situation though, because it's not screwing Homura. She is just like Sayaka, Kyouko, and everyone else in that she wishes for one thing and secretly wants another, and that causes her distress. Wishes also seem to follow the karmic flow of the universe and cause distortions. Homura not being able to change Madoka's fate is thematically appropriate.
I did always figure that Wally was resistant to physical attacks, one more reason Homu couldn't win. I've always thought that the whole Mitakihara team+Kyoko could have defeated Walpurgisnacht, but Homura refused to try to unite them after the 3rd timeline. It works well with her general running theme of failure: she had all the tools she needed to win, but because she kept trying to do it alone, rather than working with Mami and Sayaka when she had the chance, she was doomed to failure.
It seems to me that Homura is actually capable of changing the future, it's just that she fails to beat Walpurgis. I prefer to blame it on her inability to work with others rather that just "fate".
Homura is capable of changing the future, but not the future that actually matters: Madoka's.
I always liked the idea that Walpurgis losing to Madoka was its own will. It's the Stage-Constructing Witch. "She will continue to rotate aimlessly throughout the world until she completely changes the whole of this age into a drama." It looks at Madoka and finds that a selfless sacrifice against all odds makes for a good death. When Madoka died rather than let the rampage continue, Walpurgis could have pushed through the injury, but instead sort of... gave up. It had turned the world into a drama, the drama of the unlikely valiant hero who gave her life to defeat a force incomprehensibly greater than she, and it didn't mind perishing.
As for why it doesn't do the same for Homura? Well, we know from HN Elly that witches can read their victims to some degree. Perhaps Walpurgis sees in Homura the potential for a more interesting tragedy, and hence, refuses to die just yet.
Or I could be talking completely out of my arse and it really is just a matter of vulnerabilities.
That characterization of Walpurgis is a neat one, but the same write-ups you're sourcing also reference a desire to cover the world in magic and completely erase all sad and tragic things by way of making them a mere performance.
The way I saw it, Walpurgis comes to places, causes DRAMA, then retreats. In some timelines where she was seemingly destroyed, she might have faked it and retreated after being satisfied with enough destruction. I also like the headcanon that she comes to places to absorb witches, and then leave. The huge congregation of witches in Mitakihara attracted her, and thus she came.
