The Mariah comparisons are fruitless and incorrect. She has nothing on Mariah when Mariah was her age and I doubt she'll follow the same path to legend... very few do. She's obviously a talented singer, but she has awful diction and doesn't seem to be able to connect her voice melodically with the song. Random vocal runs and melisma can sound amazing and really add depth, but Ariana seems more focused on running up and down her vocal chords like Jessie J than actually listening to the music.
Watching her perform...she is no musical artiste. She obviously doesn't live and breath through her music, she seems more interested in showing off. She's a manufactured pop princess who, as others said, has grown up in an opportunistic setting. It's a shame because there are unknown singers who could belt her off the stage struggling to get their voice out.