Yes, I think the test is flawed, but not as much as people might think.
Psychology tests and trends measure general and perhaps more apt guidelines of one's personal expression. They're not tell-tales, and they are by no means anywhere close to pipe lining people into a profession which in these times is anywhere close to generating success, much less satisfaction.
They're a guide, nothing more. Based on personal experience, I think they're a fairly good guide. As a manager, however, I contended with folks from widely varying backgrounds, many of them struggling to keep pace in their primary duties while learning their ancillary skills who were often rather phenomenal in totally unidentified skills! I was very frustrated at times by not being able to place employee x in slot x when he would have been a star performer in slot x.
Ugh.
And I myself felt rather hampered by a machine which strove to rather unintelligenty "round out" it's employees with little regard to either the employee's strengths or the company's needs.
So, in my mind, it's a guide, and a good one at that. If anything, it helps weed out the obviously ridiculous professions for which the individual has no business pursuing. But it's by no means a panacea, pigeon-holing people into occupations in which they really don't belong.
In my opinion and expertise, an individual's life-long "best fit" involves all of three things: innate competence/experience, education, and desire. Lacking one of these two they'll make do, but it won't be a best fit, by any means. Lacking two of the three, they my yet be the most competent, but it'll be a disaster because it's just not where they belong.