Kind of dumb of belift but I get why they'd do it but this is clearly not going anywhere and is just a threat for show. They are getting crucified and nothing they try when it comes to media play is working. In kpop the 'denial' is normally promises of lawsuits so the public think there must not be anything to it which is why they are going to court, problem is this has gone far beyond that and more proof is coming up each day so ofc no-one believes them but their shooters, honestly I doubt they will actually make it to court because that'd be a dumb move from belift (but then again when haven't they been dumb). I feel like they are making the case now because MHJ is no longer in charge of Ador, and as the legal owner of newjeans IP, its Adors job to launch any such claims. They are trying to get this settled in court before any case of newjeans leaving Hybe/Ador in hopes the court will side with them and they can media play that to death. Thing is, they are filing for interference with business and defamation, but she was far from the first to make such claims and her trying to settle it in private whilst doing her director duty is all going to help her immensely. Not to mention all the proof docs are coming from whistleblowers, which are legally protected and for interference with business you need to show use of unlawful means, intention to injure and actual damages which is gonna be hard when she has tried to settle it internally, made statements trying to protect the illit members, pointed out what was obvious to literally everyone from the moment illit debuted (to the point that articles from actual journalists were mistaking them) and how do you show lost potentially from a group from an unpopular show who had plagiarism claims since debut. Not like they can say they would have been the next newjeans or izone.
MHJ and team bunnies don't seem to see this lawsuit as attention worthy right now, their main focus is getting newjeans out of Hybe or getting MHJ back in charge, pointing out the plagiarism was just a means to an end and they've already started moves towards their endgame. Even if the case gets a court date quickly, its likely going to be postponed because of all the other MHJ suits as the cases are interconnected. Even then, its unlikely to really get a footing because she made the initial claims as head of Ador, when it was legally her job to do so.
As for the defamation...well there are two branches, defamation publicly of facts and defamation publicly of false facts. So they'd need to first prove they didn't plagiarise or end up proving that not only did they plagiarise and open themselves up to claims based on that, but paid to admit they plagiarised.