If you actually believe that, go ahead and pick the ten companies you think are worth something, and I'll take the "unpromising" part of the batch. We can put a five year bet into longbets that the top ten companies of my group will outperform your ten companies, as scored by either exit value or value of last round raised.
Picking winners is hard, and most great companies today looked dramatically different when they were first getting started.
One possible option: no accelerator at all. YC doesn’t fund you that much, and you don’t need a demo day to pitch investors. The network and advice can come others ways too: from working for startups, and increasingly online (see YCs own startup school).
Of course this discounts other benefits of YC, but those are arguably becoming less useful as the batches have been diluted with so many lackluster startups. At this point YC almost seems like something people do not for their startups, but for themselves. It attracts prestige collectors that are more concerned with how they look on paper than how they perform in reality.
"really, a company that is renting out air mattresses" "another Digg clone" "sync my folders? there are a million tools for that"
Though your knee-jerk reaction is correct, it is specifically this which makes YC stand-out. They often seem to pick the things that don't seem promising, and yet those turn in to stand-out successes.