Public schools and media are a huge part of the problem with people not reaching their full potential.
However, in general, IQ is a measurement of potential. As with most things, its distribution is represented by a standard distribution or bell curve.
You can, and people do, argue that our present IQ tests do not fully measure human potential. Personally, I would greatly prefer it if these naysayers were right, and I believe in one sense they are. IQ measures only one aspect of human potential. Unfortunately, we have many decades of evidence that indicates that, while not perfect, IQ measures “something” that is absolutely critical to performance in the modern economy. And that criticality is increasing, not decreasing, with technological advancement.
Claims otherwise are the equivalent of insisting, per Lake Woebegone, that “all the children are above average.”
To specifically address your point, modern education ensures that a great many people don’t reach their full potential. However, even an ideal educational system is not capable of bringing people to a point where they achieve above their potential.
Our modern system tries it’s best to dumb down those who would be above average because it is set up for the lowest common denominator.