I don't think this is a very valuable way to think about IQ. It is what it is, nothing more nothing less. It's the location you fall on in a normal distribution of intelligence as measured by specific tests.
Peterson also says that it doesn't matter which questions you use. People with hi scores on one test will typically have high scores on the other tests.
It seems to be a hard thing for intelligent creatures to hear:
There are some smarter that you and some less smart and you are most likely in the middle range somewhere.
It isn't "Mental Horsepower" though. If something called "Mental Horsepower" or "General Intelligence" exist which I don't personally buy, IQ probably correlates with them but it isn't them.
IQ is a location on the point of a normalized distribution of scores on a specific set of tests. Nothing more, nothing less.
Correlations don't guarantee things to be true. If IQ correlates strongly with "Mental Horsepower" it could still be very possible for a specific individual to have high IQ with low "Mental Horsepower" although it is statistically less likely.
This always seemed to me like an important piece of social intelligence. I've noticed that people who are intelligent enough to be smarter than most around them, but who take that to mean nobody else is as smart as they are, end up getting played a lot by other folks who recognize this failure.
You could very reasonably label the outcome of that test a movement quotient.
It doesn't mean you aren't going to see big differences in results when you test it which is why they do it.