I guess to me the teaching moment isn't lost at all - we still deal with the surprise of finding out that something we expected to happen won't be happening. How is it any different than me finding out the same information as an adult here on the Dis? Aren't we ALL here for this exact type of planning advice and don't most of us do that same type of research for ANY vacation we're planning for the most part?
We still have the moment of disappointment, the "Hey, there's still plenty of stuff to do" talk just like you (somewhat condescendingly) referred to in your post, but we have it ahead of time instead of in the park. And
probably she'd say, "WTG Mom for finding out so we can adjust our touring plans & expectations around it." (cuz that's the kind of kid she is - she finds gratitude in every moment) I'm not teaching her to NOT handle disappointment, I'm teaching her the value of preparedness & planning.
If we DIDN'T know ahead of time & got to the park & found out, it still wouldn't be a biggie..... she still wouldn't have a fit or embarrassing public meltdown because my parenting style isn't lacking as you suggested. She's a well rounded, good humored child who knows how to roll with the punches & see the sunny side of things.... but that doesn't de-value sharing information with her ahead of time to ensure she has as great of a vacation as possible & making the most of every minute.
Like you said though, to each their own.