I could see it going that route as well, but I do think that there is the possibility that Petunia would try to live vicariously through Dudley like she couldn't with her sister. Having her son show up Harry in the wizarding world could be a form of revenge against her sister. I do believe that Petunia would have a lot harder time treating Dudley the same as Harry because she's had eleven years of doting and seeing him as her darling child. Harry was unwanted from the beginning.