I'm more willing to suspend disbelief when it doesn't coincide with a political agenda. Strip away the guns and Wind River is typical left-wing Hollywood fare criticizing rural lifestyles and calling for bigger government.
The villains could just as easily have been truck drivers, mechanics, or (statistically the most likely) fellow Native Americans. But they were gun-toting blue collar workers in the mineral extraction business. And the solution is apparently for the admittedly ill-prepared FBI to double-down enforcement on reservations?