Yes, G-LOC can be a cause for a pilot to loose control of the aircraft. In a flight which (for that phase) seemed to be intended as primarily straight and level, something unusual had to cause the high G. Prevent that, and you've prevented the G-LOC. A pilot who knows that they are about to enter a high G maneuver, can plan for that event. A pilot who is surprized by it may have a much reduced tolerance...