The questionnaire isn't great, but it's enough. It's also fine that the result is parroting your self-perceptions back at you, because the four letters it gives you aren't supposed to shock you with some big reveal about how you're not who you think you are.
The point is to break down what you already know about yourself into a manageable set of basic elements that can be used as a basis for understanding how your style of thinking and experiencing fits together. From there, it becomes easier to figure out ways to better manage yourself and relate to others.
For example, I knew for a long time that I didn't like socializing with large groups or heavily structured environments, and put no stock in any forms of tradition or authority without some practical legitimacy. I didn't know why. I just had these instinctual reactions to certain situations that formed a pattern. I had no idea how to relate these things about me to people who were different from me, because I had no basis from which to understand thought structures opposite from my own. And this was a big deal for me, because I function VERY differently from most people. I'm an INXP. Wedged right in-between the two least common types. Especially where I grew up, I might as well have been an alien.
Yeah, it's not **science**, but it would have been pretty fucking useful in high school to understand, for one major example, that establishment of pecking order is of highest priority to SJ's. Meanwhile, my type doesn't even have a concept of pecking order, and it naturally feels unfriendly to me to treat anyone as more or less than equal. So when half the people in the fucking school came at me with challenges, I didn't understand why. I thought I'd done something to piss them off, and responded with my version of friendliness, which was to treat them as equal. I was never interested in fighting for any reason, least of all personal satisfaction. My obsessive self-analyzation would never allow me to do anything so selfish. As a result, I endlessly infuriated every SJ in the school and was bullied ruthlessly through most of my public education. I couldn't figure that shit out for years afterwards, until I discovered MBTI and came to understand how SJs function.
And it's most certainly better than some bullshit about how your destiny is tied to the alignment of the planets on the day you were born or something. Comparing it to horoscopes is pretty far out there.