Defining it that way doesn't exclude ordinary people. That's an erroneous claim on your part.
Humans as a class exhibit certain capabilities. Thus we expect a class of algorithm to either roughly meet or exceed those capabilities across the board in order to be considered "general". It is clear that we have not yet achieved that.
First, what is your definition exactly? That it must be better than the median human intelligence?
You're trying to define a term in a way that's completely detached from how anyone uses it. If we discover an alien race with an IQ of 95, people aren't going to say they don't have general intelligence.
We haven't defined an exact cutoff for what counts as general intelligence, but it has to include regular people with an IQ in the 70s that don't have a serious mental disability. If an AI can do every single cognitive task as well as a stupid person, it would have to qualify as having general intelligence if the stupid person qualified. It doesn't matter if the AI beats the median person 0% of the time, as long as it beats someone who is considered to have general intelligence at the task.