I actually think melody does more than we think on tracks with certain harmonies you know its not jus nicole doing them, even though the camera stays on her.
Melody is all over the harmonies in this song..

I guess the label think it will inbalance the group to have just two main singers in the group so they stuck with one.

The reason they originally searched for a new pussycat doll was so they could have 3 strong singers which would've been Nicole, Melody and Asia(if she didn't reject the prize of becoming a doll).

2b honest if all the girls could sing there would be a few more harmonies in their songs. U hardly hear more than 2-part harmonies sometimes 3 in the songs they sing.
Alot of backings live are in unison or just melody harmonising with Nicole...

Nicole is not great with harmonies as u've heard from solo projects but good with leads, so Melody has that main job unfortunately of gettin harmonies on point.

Video cool and song nice actually