Earlier quoted context omitted.
Strictly speaking you are right, my logic was flawed (hidden assumption). But let's stick with the orignal issue here, which is whether the test is predictive.
Agreed - this is why I asked whether there is any proof of its alleged predictive power. Without this, I don't think it's reasonable to assume that it is in fact predictive.
For example, the simple test of whether a user clicks a certain link or not already has predicitive power (companies are using this, fruitfully). So a more sophisticated test like MBTI certainly has some predictive power.