Hayley has a good voice, but Bleeding Love and I Have Nothing don't suit her voice. There are many who sound like her, but that does not take away from her talent.She delivers a vocal well, and that is as important as the voice itself being pleasing.
There are also a lot of girls who sound like Leona and have her range, however, very few have her consistency of tone and pitch or her technical ability. These things set her apart.She rarely goes far off pitch or falls of the melody when riffing/runs/whatever you care to call melismatic prnamental passages.She rarely sounds screechy or oversings.Some people may not like the eccessive melisma/thin tone/high notes, but others love it or overlook it because there is so much else to her vocals that they love.
I could happily listen to either of them if they were/are performing a song I liked and the song suited their voice.