Most of those interview questions, don't really have much to do with the way someone actually works. I just went through one of those SV gauntlets at a YC startup, and got a yes, but at no point I thought any of the interviews were any good: Not enough time to actually learn about the interviewer, or solve a problem that a recent graduate couldn't solve. I know some awesome people that wouldn't have passed my interview, and I know people I'd never want to work with that would have passed.
The whole thing made me see why the situation in SV is so screwed up: If we can't really ask for things that show real experience levels, and it's all about short term first impressions, set by interviewers that aren't even necessarily any good at interviewing, how can we improve?
I've always much preferred interviews that asked for the same amount of time, but where people could show a picture of their real output, instead of a little puzzle.
Imagine you are hiring a chef to man your restaurant, and what you ask him to do is get through Chopped: Give him secret ingredients, and ask to make a dish using all of them in 15-20 minutes. You'll be testing something: Some people will do better than others. But are the things you are testing really going to matter, in practice, when what a chef really has to do quickly is to execute a well known, practiced menu, along with kitchen management skills?
We don't test for the things we do at jobs, and therefore, we can't hire. Not a surprise.