[vzcx]

I don't think that's at question in this case. It was decided in Massachusetts v. EPA that EPA is required to make that determination itself. Three years after that decision, EPA basically answered "we think it is."

The court isn't bringing any of that up in this opinion. They are looking only at whether Congress specifically delegated EPA the power to regulate emissions by means of "generation shifting". The majority opinion was "no, they didn't."