Just because Neil Gorsuch sincerely believes something doesn't mean it's true or a good idea. A lot of Neil Gorsuch's sincere beliefs are absolutely bonkers. (I'd love to hear an absolutist "constitutional conservative" argument against his approach to Indian law, though; that is an area in which it is the right whose jurisprudence has traditionally been "the government can do whatever the hell it wants and dare people to try to get it to stop.") I do agree that "hack" is manifestly not the right word for him, though.
FWIW Clarence Thomas's view is that the Indian Citizenship Act of 1924 rendered all tribal treaties and agreements null and void, and thus now all Reservations and federal recognition of tribes is illegal.