I think that one problem is age. Wendy Darling is supposed to be, what, nine? Since Disney can't hire anyone that young to play the part, they hire an actress who then acts that young. If she doesn't look nine to adults, she did to my DD6. In fact, on her sixth birthday, she ran into two Wendys, one at CRT and one outside POC. The one outside of POC was with Peter Pan, also way too old. DD6 told Wendy that she didn't need her autograph (she just got Peter's) because she had already signed the book this morning. That Wendy was on the ball enough to go along with this.
If you look at DD6's autograph books (the expensive type, darn it, with places for pictures next to each autograph), you can see that she saw two different Cinderellas, two different Auroras, and two different Belles. They were the characters to her, and if she ever saw a difference, she never mentioned it.
They are acting parts. Sometimes they might not look exactly right, but it isn't really how they look, it's how they project the part. On our last trip, we didn't see one that wasn't convincing to DD6.