Under the most common systems, IQs have a standard deviation of 15 or 16 (the two most common measures use 15 and 16, some use different systems) points and a mean of 100. I’m not sure if you were under the impression that IQ is defined by some natural measure, but it’s not. They’re defined by the system that’s being used to measure. IQ is 100% relative.
We normally define Genius as 3 standard deviations from the norm, but I’ve also heard 3.33. If we go with 3 that means 0.135% of people are geniuses. If we go with 3.33 then 0.0434% of people are geniuses.
Commonly 1 standard deviation from the mean is the “normal” range. Though someone 2 standard deviations above the mean isn’t all that special really. But if you took someone 1 standard deviation below the mean and someone 1 standard deviation above I believe almost certainly if you talked to both of them for 20 minutes you’d easily be able to tell the difference between them. In terms of their abilities, someone who is one sd below the mean would struggle tremendously in the typical gamut of AP courses, while someone who is one sd above should be totally fine.
Well, the majority of Janitors and a large portion of Doctors (more than 25%, less than 50%, can’t tell more than that from the graphic) fall into “normal” so if nothing else that should show how vast a region “normal” is.