YC runs a free, online Startup School each year. All of the videos are available at https://www.startupschool.org/ Watch them, and see if you learn anything.

The actual onsite program has an acceptance rate in single digit percentage. The last invitation-only Demo Day held at the Computer History Museum was completely full. See https://techcrunch.com/2018/08/20/here-are-the-63-startups-t... and https://techcrunch.com/2018/08/21/all-59-startups-that-launc...

So yes to all of your questions: great education; great connections to alumni; great connections to VCs and mentors; and YC staff have tons of experience.