The AFQT is used ONLY to determine your joining or not. Not what jobs you qualify for once you join.
While the AFQT is determined from only a portion of the subtests, those other subtests may be what the specific job (AFCS) you are looking for needs for you to qualify for it.
Find out what particular job you are interested in and then find out it's requirements. Air Force uses a composite score system called MAGE.
Computed from the Mechanical Comprehension, General Science, and Auto and Shop sub-tests of the ASVAB.
This score is computed from the Numerical Operations, Coding Speed, Word Knowledge and Paragraph Comprehension portions of the ASVAB
Derived from the Word Knowledge, Paragraph Comprehension and Arithmetic Reasoning sub-tests of the ASVAB.
This composite is derived from the Arithmetic Reasoning, Mathematics Knowledge, Electronics Information and General Science sub-tests of the ASVAB.
For example, to be a Boom Operator, those guys who do the Mid-air refueling of other aircraft... you need a G of 55 or higher. Among many other requirements.
If your goal is simply to join and you could care less what specific jobs you qualify for... By all means, concentrate only on those subtests in which the AFQT score is derived. Otherwise concentrate on those IN ADDITION to those which matter for the job you want.