Sorry if you think I'm insulting anyone but the fact of the matter is that Fantasia can outsing Diana. Diana might be able to outscream Fantasia but that's a whole other debate. Even Randy, a big Diana fan, told her that she has problems with lower notes. Fantasia, OTOH, actually hits notes in every register.
Singing should not be defined as who can sustain the loudest, longest glorynote. That's what Diana DeGarmo does. Is she a horrible singer? No. Is she good enough to be the American Idol? No. She tries to sing like Kelly Clarkson but doesn't come close.