You’re likely correct that the horse, in full panic mode, failed to see the fence. Adding a visual cue was one of my suggestions.
That does not, however, preclude using electric as a “memory aid” for the horse. Horses have excellent memories and are very aware of their surroundings. Maybe in a full panic their memory would be overwhelmed by their fear but in less stressful moments (as in “horse play” or just grazing) the residual memory of being “bitten” by the fence might prevent a less serious encounter.
It’s really not an “either/or” situation.
G.