Does it make more sense to say that intelligence is 'multi-dimensional' or to say that it's 'adimensional'? After all, IQ is a metric, not a direct measurement, as intelligence isn't itself directly observable. If we're defining 'intelligence' as being a quality of the human mind that's conducive to success at achieving one's goals, then it becomes something of a tautology to simply ascribe that quality to people who have observably achieved their goals.
If the IQ metric is intended to correlate success on certain types of tests with success in other contexts, then it may be reliable in certain regards - e.g. people with higher IQs do tend to hive higher incomes, as 3pt14159 pointed out below - but the actual nature of that common causality is still something that may not itself be understood sufficiently to describe it in terms of dimensionality.
I've always thought of intelligence as the ability to learn, which you could say is the maximum speed you can gain knowledge and understanding. A person may be able to learn in some areas very well, but not so well in others. Also, someone who has devoted much time to gaining knowledge and understanding may be much less intelligent as someone who could learn quickly but never puts their mind to it.
An analogy for this view of intelligence and knowledge is like a car's acceleration and speed. Some cars may be able to go very fast but they may take a while to accelerate.
As others have mentioned in this thread, what obviously matters more is how you apply intelligence, knowledge and understanding.
If the IQ metric is intended to correlate success on certain types of tests with success in other contexts, then it may be reliable in certain regards - e.g. people with higher IQs do tend to hive higher incomes, as 3pt14159 pointed out below - but the actual nature of that common causality is still something that may not itself be understood sufficiently to describe it in terms of dimensionality.