It is not intended as a measure of giftedness. It is intended to measure proper cognitive functioning. In pop culture it is often talked about as a measure of genius.

I think it is a legitimate measure of giftedness at the top end. Genius, not so much.

Having an IQ of, say, 160 means you're extraordinarily capable of a broad range of cognitive tasks. It's more than merely proper cognitive functioning. But it doesn't mean you will be a world-altering genius. There are many stories of people with staggering IQs who ended up doing nothing notable, or producing a lot of interesting and odd ideas that ultimately had no impact on the world.