Demi has a great voice, but doesn't a "voice" have to reach out to millions to be apart of a "Trinity"? Because I could name any random artist with a good or big voice. There are plenty of flops with great/big voices.
Whitney, Celine, Mariah and those other girls are/were instantly recognizable voices, not just good or great voices.
And to be honest.. if we really wanted to get technical.. Adele would really only be the "voice" of this generation I could def she her in the league of the 90's gerls..