Imagine working for Inhance and high-fiving your coworkers because a court said it's legal for you to continue contaminating humans and the environment with a harmful chemical.
What kind of sick motherfucker sleeps well after that?
Not really. The argument came down to the Section 5 definition of "new", since other arguments were ignored as moot. It was a typical pro business decision that argued on semantics instead of law.
The court even signaled that they would reject it under Section 6 if EPA were to use it due to the need "to weigh the costs to businesses and the overall economy before shutting down an ongoing manufacturing process".
If they have had this process for decades it's not new though, the information about the harms is new. You could argue the EPA doesn't have enough power when something is provably toxic but this ruling isn't surprising, especially when it would create significant case law