Beyonce isn't really trying to ape Mariah, especially these days. Beyonce makes music that's designed to mix the political and the personal, music that explores the disconnect between her being America's Pop Sweetheart and being a Black woman, between being a powerful diva and her complicity in gender roles that make her happy. Mariah's more like the goofy, fun, charming girl next door.
Mariah's brand of conspicous consumerism is bling and glitter, diva stereotypes. Beyonce approaches the concept of wealth more like a hedge fund manager.
I love them both for different reasons: Beyonce could never sing a line like "not even a nail technician with a whole lot of gel and acrylic could bring us back together again" and make it sound better than it looks written down; but Mariah could never be convincingly sexy like Partition.