I assume YC mainly selects by first looking at the potential market and the team. The idea itself is less important. If 'only' the founders will stick together, work hard, learn fast and are adaptable.

A good team (history, education, friendship, track record, focused, balanced, ...) in a potential huge market is worth the gamble. Ideally the setup (I guess) 'only' needs a lot of money to make the difference. Because money will then be available in large quantities.