No you're definitely not being naive and your expectation isn't unreasonable.
Before I ever started umpiring I was a baseball nerd and I had actually read the rulebook through. I got into umpiring a little over 2 years ago when I was 15. I primarily do LL games, but not as a volunteer for LL. Pretty much all of the local Little League's here use our association to cover their games. Before I got put on any games I went to 5 class room sessions, a field session, and 2 supervised scrimmage games. Then my first season I did mostly low level minors games, with experienced umpires. I feel that I had a pretty thorough training. Since then I've read and watched a ton of helpful resources online, and I make it a point when I work with veteran umpires to ask them for feedback and any advice they have. Yes my question was rather ignorant and I willingly admit that I should have already known it. I'll learn from it, which is what I always try to do whenever something happens in a game.