Surely this argument comes down to generalisations :

Example: INTj's are socially disadvantaged - true or false

True: socionoics points this out and it's fairly visible if you have ever met many INTj's, if it's true, its true, lets not pretend its not true to to make the world a more just place.

False: Any person can become socially competent if they work at it and try, we can all learn to be good at something, so it would not be supprising to find some very socially competent INTj's.

The point is, a person is very complicated with many driving forces acting on them, so socionics can only hope to judge statistically. Please, that is a very important word, socionics tells us about people statistically and groups behaviours etc together statistically to form the 16 types. Anyone can become a teacher, but statistically some types will find it easier, more satisfying and a better choice of career than other types, remember, I am saying that statistically

@Diana: I think you are right that doing what you enjoy is better than doing what you are good at, but I think it's important to note that there is a very strong link between the two, in the vast majority of cases, people enjoy doing what they are good at, and dislike doing things that they are particularly bad at. This is a well established idea in psychology.