I couldn't agree more. I had the PM title twice before I worked with some senior PMs at a very successful Fortune 50. What a difference experience makes. I cringe when I think about how incompetent I was in my first two PM roles.
Ditto. My first three stints (albeit with zero help from peers or mentors) were terrible. It seems like you need a couple of epic screwups under your belt before the patterns start to present themselves.