To be neutral about this topic in general, tribal lands/reservations have their own laws and law enforcement officers. It’s best that anyone traveling through such lands follow laws/regulations to a “T”.
Lawyers must be approved to practice in tribal courts just like in state courts and federal courts. Most, if not all, lawyers will not go through the regulations of getting approved, because tribal laws are completely different than state laws.
A downside to this Supreme Court ruling (if any), is that criminal defense attorneys must either learn the local tribal laws, which vary from tribe to tribe, or just not represent any individual charged in a tribal court. Even sadder is that members of a tribe who get into trouble might not even be able to find a defense attorney to represent themselves.