As an interviewer, I gave one pretty simple task (people solved it in as little as 8 minutes), wasn't using any real CS, even though I'm good at it.

The reason was that aboint 70% of candidates couldn't write a simple loop -- to filter those out. The actual solution didn't matter much, I gave a binary decision. The actual conversation matters more.

This. Main point of giving candidates CS problems was always to weed out those who couldn't program at all, but somehow were still in the industry. I worked with such people - it's unpleasant.

Somehow someone figured that giving harder problems should result in better candidates. Personally, despite having passed most of the tests I've been subjected to, I don't see the connection.