Whilst a lot of people are critical of the length of time taken to get everybody off, I actually think 3 hours was pretty good from my experience of dealing with major incidents. Looking at those damaged cars at the station, getting the cars hauled back in was never going to happen quickly. So I'm actually prepared to give Disney some slack there. Whilst not pleasant for those on board, I can't be too critical of the time to respond. Although sounds like communications could have been better (but again, that is no surprise to me - in the middle of an incident, communications are crucial, and lack of information is very common - in both directions).
Now, you may question the wisdom of having cars with no AC in them, for breakdowns in the sun in the middle of the day. But I believe that there is emergency cooling in each car that can operate for 4 hours (if what I read further up the thread is true). So if the cars get evacuated in 3 hours, that 4 hour emergency cooling should be adequate. So again, I'm not too critical of Disney here.