My technical ability is readily apparent to those who have viewed my work, and by virtue of those who have praised it. I don't claim to be the best programmer in the world, just a competent one. I've also been programming for over 20 years, that might have something to do with it.
However, I suck at interviews, in any way shape or form (personality tests, technical tests, you name it). Yet I've aced every job ever given to me, and people love to work with me (even in spite of my salty attitude).
To think that you can determine what it is like to work with me over the span of a year within the span of an hour is completely and utterly ridiculous.
As it turns out, the little sub-problems they give are the most trivial part of programming. The hard part, the part it takes many years to get any good at, is coherently organizing, documenting, and ensuring the stability of a larger system, particularly concurrently with other programmers. Or designing an algorithm that you can't just Google. Or making a really tough decision about what features to cut or what direction to pivot. Or organizing a vision of what will add the most value for the customer. Or...etc
Being an introvert with a monotone voice, general lack of expression, and deadpan sarcastic humor does wonders for personality tests. Most people's default reaction to me (in interviews or otherwise) is that I am a total dick. Which I am, but the kind you don't mind hanging around.
I don't do well with programming that has a one hour deadline. But give me a day and I can produce the typical output a programmer would within a day.
If I spent all my time practicing for interviews, I'd probably be better at them (with stuff like Top Coder or Interview Cake or whatever). And I think giving these things a whirl is well worth it (not for the sake of winning in interviews). But it is not my life goal to be good at interviews. It is my goal to work in areas I am interested, and continue learning things that are directly relevant to my real-world tasks (sorry, writing a red-black tree on a white board within an hour never happens to me in the real world).