I mean something like "New Avengers" did need to happen. Johns and Austen had been doing Avengers with basically Busiek's cast, which was pretty much the same core cast the book had had since the '60s, and readers were burned out on these characters. Wanda was one of several characters who had been in the book too long and needed to take a rest. "Disassembled" sucked as a story and I think even many fans of Bendis's work admit that (plus the art and color is really dated now) but I don't think "Avengers" would be a global franchise now without it. So it wasn't a mistake, just a stupid story (though I guess stupid stories are mistakes even if they lead to something good).
It just so happens though that Wanda got hit really hard by being the villain of that story and then even harder by the "House of M" ending that forced her out of comics for many years. I would actually like to see how she would be written as part of the modern Avengers, but for a bunch of reasons it's never happened.