You've illustrated its misuse well. S and N have different styles of creativity. N is not more creative. Unfortunately many of the creativity tests were developed by Ns,a s were tests of giftedness, so there's a bias that puts one preference over the other. The question isn't which type is the best leader, or the most creative, or the best teacher, etc., but in which way does each type achieve excellence in those areas. Check Marci Segal's work on creativity..
Suppose we grant that the Intuitive is not more creative than a sensor by definition. By implication, it would follow that the Extrovert is not more outgoing than the introvert by definition. Simply put, both sensors and intuitives engage in creativity, but they have different ways of doing so. Similarly, both Extrovert and Introvert can be outgoing, yet they simply go about it differently.
Very well, however, the MBTI folks will then ask, why is it the case that more Extroverts are outgoing than Introverts? An advocate of your typological method will claim that perhaps social outings are biased in favor of introverts and discourage them from being active in interpersonal activities.
I think this is rather plausible. Any shy and reserved person is likely to be labelled as an introvert. In many cases, indeed taking a different approach to encouraging people to socialize can be successful; that is, a method that often inspires an outgoing person to interact with others is ineffective once applied to introverts. However, a new method could be designed specifically for helping reserved people to become more adept at interacting with people.
I admit that this does solve the problem of unwarranted personality labels advanced by the MBTI authors, as it suggests that one type of personality can master the skill-set that a different type is expected to have.
Regrettably, it runs into difficulties at a further stage of inquiry. Although in many cases a person's MBTI test-results are based on a person's life-experiences led him to perceive himself and are irrelevant to his temperament or innate dispositions. In other cases a person's temperament has a great deal to do with the MBTI persona he identifies with. For instance, a person who is of the introverted temperament is frequently led to 'type' himself as an introvert.
Empirical studies have shown that Introverts by their nature tend to become more easily stimulated than extroverts and therefore tend to require less interaction. On that note, I do not believe that you can avoid conceding that there is something about the MBTI definition of the Extrovert that makes him better adjusted to be outgoing than the Introvert.
This fact does not show that Introverts are necessarily less talented at being outgoing or less talented at doing so, however, it does imply that there is a certain inequality between types. Some are by their nature drawn to one kind of an activity and others to another. As for example, an introvert, by the constitution of his mind is subtly drawn away from activities of high social interaction. He certainly can fight this natural tendency and become more outgoing than any Extrovert, however, he will have one certain hindrance that the Extrovert shall lack.
The implication of the temperament perspective on the issue shows that at least in some cases, a person of one MBTI type is going to be at a disadvantage to learn a certain set of skills that the person of the other type will not. Although the disadvantage is far from insurmountable, it contradicts the thesis that in all cases all MBTI types have equal strength, as can be exemplified by the dictum that sensors are not less creative then intuitives, introverts not less outgoing than extroverts and so forth.
In summary, by definition one type does not have a virtue that the other lacks, as a type in this context is a temperament which is nothing but a tendency. However, in the context of your argument, a type is not defined as a temperament, but a collection of personality qualities. As noted, in some cases, a person's temperament will influence his personality profile and manifest in existence or lack thereof of certain qualities that are present in another personality profile. If you claim that extroverts are not inherently better socializers than introverts but are so because of a certain social biases inherent in our society, the argument from temperament still holds. Even if Introverts are given a fair opportunity to become better socializers, they will be hindered by their natural dispositions. In that respect, it is a mistake to claim that all types have equal strength.