i think it depends on what the idol did. there are different types of bullying. some are physical and others are emotional bullying.
if there was physical damage involved, such as injury involved, or severe incident that affected the vimtim psychologically, then there should be reprecussions.
however losing a career over it? its a bit harsh imo. these things should be sorted out in privaate and the idol should apologize, to the victim personally. and also issue a public apology.
however I dont know the exact details of Soojins bullying case, so I dont know if she really deserved it (I havent got the exact info)
revenge is a petty thing as well. and I think its a short term solution to a deeper problem. the victims mental health wont magically improve if she gets her bully fired from her job.
Idols also depends on public persona, so this is why the company thought it was the right decision I guess.