One of the worst prejudices of idols that idols want to break is that they cannot sing well enough to debut as a solo.
It's true that when performing in a group lifts some weight off, however, it doesn't mean they are not capable of singing solo. The bias started by idol groups who really didn't have any talent to sing live. Their horrible example grew to be a prejudice judging almost all the groups.
However, slowly, as groups who try to prove themselves of ability appeared and people started to look at them without any bias thought. Not all girls did have talent in singing, but if they couldn't sing as much as a solo vocalist, they were able to dance or rap and try their hardest to sing at least to average.
While there were girls who tried hard or had talent in something else, there were girls, the main vocals of groups, who completely broke the prejudices.
1st - YuJu of GFriend
2nd - JiHyo of TWICE
3rd - Wendy of Red Velvet
4th - EunJi of Apink
5th - MinAh of Girl's Day
6th - SolJi of EXID
7th - Solar of Mamamoo
8th - TaeYeon of SNSD