In the entertainment industry an actress is waaay above an idol in terms of hierarchy
Guess who will people believe more
but the main problem for soojin isn't that its an actress. Unlike alot of the others who have a mix between old classmates defending and accusing, the only people coming out atm for her are accusing. It's all so one sided that unlike the others where there is some fans believing the idols (leaving the general public interested to decide to wait for more info) none of her fans in Korea are believing in her anymore.
It being up against an actress gave the story loads more media attention for sure, but it wouldn't be as bad as it is now if she had at least 1 person from her school days on her side. Then it would have turned into a who's telling the truth battle, and with that people would have trusted the actress since she had more to loose (being higher in the hierarchy and all that).