Wanda's fans are lucky that the Fox X-Men movies never used Wanda and Pietro as members of the Brotherhood or (until their version of Quicksilver) Magneto's children. If they had asked for Scarlet Witch and Quicksilver to be included in the original deal, they probably could have got exclusive rights easily, since an Avengers movie seemed impossible back then.
Because of the X-Men cartoons and the failure of the one Avengers cartoon with Wanda in it (and her and Pietro not being allowed to appear in Avengers: Earth's Mightiest Heroes), I think they were actually better known to the public as X-Men characters, and I remember people being surprised at the announcement that the MCU was going to use them.
That may help explain why so many people thought this show was going to introduce mutants, even before they pulled the bait-and-switch with Evan Peters.