Well, if treated as anything other than something to do for kicks then yes, they’re for stupid people. In order to have any value at all, an IQ test must be properly and professionally designed, calibrated, and administered. Anything you find online should be taken about as seriously as you’d take a Cosmo quiz.
No, it wouldn’t. People do perform better on IQ tests now than they did decades ago (“The Flynn Effect”, a phenomenon that has yet to be explained), but the average is always 100. The tests and scoring system are recalibrated regularly to ensure this. Thousands of people take the test, and the mean score is set to 100. Scoring 100 now requires more correct answers than it did decades ago, but it’s still the mid-point of the IQ bell curve.
Back to the OP, 50% of the population does not have an above average IQ in any meaningful psychological sense. A score of 100 is the perfect mathematical average, but the average range is generally considered to be about 90-110. Roughly 50% of the population falls into this group. Only about 25% of people score higher than that.