This is kind of true, but also belies the depth of the Chevron change. In this example, plaintiffs can now, for example, challenge how the "X%" calculation is done. What's an appropriate methodology?
In the past, courts deferred to the agency: as long as it's scientifically valid + consistent, it's up to the regulator, not a judge. Now, it's up to a judge.
So if I sue and say "you should use a 0.01 alpha for calculations, not 0.05" for your X% calculation, then a judge makes the methodological decision, not the statistician.
IMO, it's not really reasonable for congress to design statistical methodologies as part of the text of a bill.
What's the process for determining the methodology? Would another process have been better? Does the plaintiff's proposed approach for methodological determination also conform to this law?
In this case, "how to go about determining methodology" is left ambiguous, and is now the province of the courts, not the EPA.
If congress wants to delegate details to experts they could explicitly state that in the law, and create their own organization of experts to do the job. Giving the president more power is not a requirement, and enforcement should remain separate. But even then, regulations shouldn't be ambiguous. The laws should state something like "food purity should be within %x of yada yada, where x is updated yearly by the appropriate agency" Then it's up to the courts to decide if the law was broken or not.
In the short term this could be a nightmare as companies flaunt all sorts of regulation, but I think overall it is a good thing.