The important question that is not typically considered is not how they test, but rather if they will be happy doing the job. People only perform well if they are doing a job that they actually like. Another issue is common misconceptions about what type of job a person will like if they test a certain way.
For instance, people look for extraversion in sales roles but highly extraverted people don't do well in sales because they are not good planners, tend to be disorganized, talk too much, doesn't listen to what the customer is saying and most importantly, get their feelings hurt too easily when people don't respond to them.
A slight introvert who is money hungry/success oriented will outperform an extrovert (high) every time unless we are speaking about high volume product sales, where the customer comes to them, such as retail sales.
Another problem is IQ. A certain MB type for someone with an IQ of 120 will perform differently than someone with the same MB type and an IQ of 100.
Lots of factors but again, what it boils down too is does that person want to do this job..and why.