Where is the successful solo singer from Spice Girls? They all released moderately successful solo albums then vanished fairly quickly; whether it was on their own or due to irrelevancy.
Musically, Mariah beats Britney hands down. No-one is going to credit Britney with impacting the sound of music as much as Mariah. But Britney belongs to a different generation where visual reigns over vocal and everything else, and so do we. Therefore it's no surprise if people do think that Britney is a bigger icon in this day and age; yet Mariah has cemented for herself an everlasting position in the canon of mainstream music that Britney can only hope to attain in time.