This alone isn't enough to tarnish Idol, but it is the start of a paradigm shift for them, and their next move is what could make or break them.
Up until now Idol's entire business strategy has been to buy themselves good optics. Give the talents upfront funding and a generous revenue cut, pay clippers, pay for debut watchalongs etc., it's been easy enough to push a clean image in front of a significant portion of the community. Even the one minor drama I remember from before this (them taking forever to pay an artist they'd commissioned) was dealt with by giving the artist a bonus iirc.
The Riro termination notice has put an end to this image, and regardless of how we on the forum may feel about the content of the announcement post there are a lot of people who feel listing her crimes was in poor taste - and that's the kind of backlash you can't buy your way out of, because the sentiment's already out there and you can't put that genie back in the bottle. Everything they do going forward is going to be much more harshly scrutinised, and I feel it's going to get the ball rolling on the general public having a much more cynical interpretation of the company's financial "generosity".
In hindsight the announcement post giving clear details about Riro's misconduct feels out of character for Idol, and I think the only reason they went public rather than giving a generic breach of contract statement was because the staff member being involved put them between a rock and a hard place. Someone would have found out about their affair anyway because of course they would, it's the internet, and if the only acknowledgement from the company was a vague talent suspension and a manager quietly leaving then it could very easily be framed as them covering up a grooming incident even if that's wildly untrue, there's no way that kind of thing would be spun charitably. Volunteering this much information themselves might come off as unprofessional in the moment, but drawing attention to the other ways that Riro stepped out of line makes it harder for her/her fans/random shitstirrers etc. to frame her as a completely innocent party being abused by a corporation, it's a much more balanced image making the company's wrongdoing (being oblivious to a member of staff participating in an inappropriate relationship) the lesser of two crimes.