A brain spike is seen as more humane than decapitation for larger animals like cattle, I imagine the same applies for fish.
And given that this method provably results in less trauma byproducts than traditional methods, there is strong evidence that this is a more humane method.
I think the modern western practice owes more to what is most convenient in industrial setting than most considerate to the last moment of consciousness or spirit. fwiw I would personally go with hypoxia over deep brain trauma, of course also hoping it matters little whatever else may or may not be in store.
And given that this method provably results in less trauma byproducts than traditional methods, there is strong evidence that this is a more humane method.