Regarding this subject, I would say it both is and it isn't.
Untrained people are generally clueless and like the example you gave, once you have a dominant position their attempts to neutralize with gouging will likely fail as you can outposition them to apply a finishing hold. An arm triangle choke is one of the best holds standing or on the ground to finish in this way as the position protects you against most of what they do to try to nullify it.
That said, there are some delusions the other way also to think that eye gouging can't be used to potentially nullify a grappler if the person is really committed to the gouge and especially if they are trained.
The biggest danger is when initiating a clinch, unless you just shoot for a double or single leg you have essentially given them an opening to gouge you by seeking or taking a grip in a standing position at close range. It may only be very transitional but nonetheless the opening is there. When we see 'accidental' eye gouges in the UFC this is usually where it occurs from.
This potentially can occur during some scrambles on the ground as well but again there many other strikes and holds that could be more effective from here.
The main data on this however comes from the history of Rough n Tumble fighting in the United States in the 18th and 19th centuries.
People may not like to hear it especially martial artists but when eye gouging was permitted and people trained for this form of combat, it indeed became the most effective and efficient way of winning the fight.
This article (which my sig comes from) details the history in depth of what was truly 'no rules whatsoever' unarmed combat, but became known as gouging matches because that emerged as the fastest and most efficient method for emerging victorious.
ejmas.com
"We found the combatants' fast clinched by the hair, and their thumbs endeavoring to force a passage into each other's eyes; while several of the bystanders were betting upon the first eye to be turned out of its socket. For some time the combatants avoided the thumb stroke with dexterity. At length they fell to the ground, and in an instant the uppermost sprung up with his antagonist's eye in his hand!!! The savage crowd applauded, while, sick with horror, we galloped away from the infernal scene."
That said, the vast majority of people are not so ferocious or trained or prepared to take it to that level which means that in most scenarios an eye gouge attempt by an untrained person from a bad position will likely fail against a trained martial artist.
