I believe the NFL has a much larger issue at hand with brain trauma/debilitating injuries/prescription med abuse/domestic abuse than the NHL.
The HBO special on the Chicago Bears 1985 Super Bowl team is the tip of the iceberg.
I don't feel qualified to say whether one sport is worse than the other with regards to causing brain injuries. They both demonstrably have a serious issue with it. I do, however, feel that ANY sports league should absolutely prioritize the health and safety of their players. One easy way to do that, in hockey, is to take unnecessary (and avoidable) hits to the head out of the game. And one very easy way to do that is to remove fighting by removing the "so called" need for it...increase penalties for serious infractions to the point where players err on the side of caution.
Caution. The operable word. Heaven forbid human beings in the 21st Century learn how to enjoy sports where players must be cautious of one another.