Why does Scout feel it wouldn't make much of a difference if Uncle Jimmy had come with Aunt Alexandra in To Kill a Mockingbird?

Scout feels that it wouldn't make much of a difference if Uncle Jimmy had come with Aunt Alexandra because, while her Aunt is forceful and opinionated, especially about Atticus's children's behavior, Uncle Jimmy "never said anything" (Chapter 13). 

Scout makes this same observation earlier in the book, at Christmastime.  She dreads the traditional Finch family get-together because of the inevitablity of tangling with Aunt Alexandra and Francis, Alexandra's grandson, who is about Scout's age.  Although Uncle Jimmy comes to this gathering too, Scout does not include him in voicing her antipathy, because "he never spoke a word to (her) in (her) life except to say, 'Get off the fence,' once" (Chapter 9).  Clearly, in Scout's mind, the presence of her innocuous Uncle is far overshadowed by his outspoken wife.