Most commentators, myself included, doubted the Supreme Court would rule on the merits in Moore. There were sound reasons for it to dismiss the case as moot. Having decided to make a point, however, the Court got it right. For once, it followed the clear mandate of history, common sense, and its own precedents and rejected the independent state legislature theory.
Justice Thomas made a reasonable argument in dissent that the case was moot. Logically, he should have stopped there. He even sort of admits that he should keep his mouth shut at that point. But he couldn’t help himself, so he told the world that he completely bought into the ISL theory. Why, other than having diarrhea of the mouth? Probably because he can see himself quoting himself as authority in some future case. He does that all the time.
The Court left the issue of the standard of Supreme Court review of state court decisions on elections for another day. It is likely that it will ultimately adopt something like an egregious error standard, based on the Kavanaugh concurrence. Since that conforms nicely with the federal due process standard, it makes sense, even though, with the current Court, it would probably only be used to help Republicans.