Conservative Justices Clarence Thomas, Samuel Alito and Neil Gorsuch dissented.
Why am I not surprised? Of course those three would go against the prevailing judicial opinion and in favor of their own partisan view.
Opposing the independent state legislature theory in the Supreme Court were not only Democratic partisans, but a vast array of election law experts, important scholars on the left and right, judges appointed by both Republicans and Democrats, and the Conference of State Chief Justices, representing the chiefs in all 50 states.
...Roberts wrote in his majority opinion: "The elections clause does not vest exclusive and independent authority in state legislatures to set the rules regarding federal elections."