No doubt leaving MK has been bad. I think that's been the narrative for a while now but it's been worse because of not having distractions such as parades or later hours). But I will say that just about everywhere I have been with large crowds leaving is just a nightmare. That's my experience but it can't mimic everyones. Doesn't make it any better for sure. What hurts Disney more in that respects is when their transportation system doesn't work as well as it can. Issues with monorails, busses and boats will make the situation much worse than it has to be-extended hrs or not if it was working like a well-oiled machine you would be able to move people quicker with less back up issues.
The last time we attempted to watch fireworks for 4th of july at the best fireworks display in our area, which is in a sprawling office park, it took 1 1/2 hrs to get out because..get this...no one was letting people make a left turn out of the various parking lots and we had made the very poor decision to park in a lot that required left turn to get out to the main road. But that place is always a mess leaving with 20,000 or more people all trying to leave at the same time right after the fireworks end. We just go watch them now from outside of the venue but there still is traffic issues we run into.
As far as the summer issue and not visiting..I want to honestly say that sort of thing can happen at any moment throughout the year. One event, one detail, one this and one that can make someone swear off something. People swore off going because of the crowds in general being soooooo bad in their eyes. People have sworn off going because the CMs were rude to them and they felt there was no magic. Every decision Disney does and well businesses in general has the potential to swear off their clientele. I just honestly don't see this summer hrs issue any less important than something that happens to someone at any other point in the year that could make them swear off Disney. But also to Pete's point....driving off at least some people...may indeed be some of Disney's point at least partially and at least to a point Disney is going to be ok with that (as businesses will as they strive for that balance).
As far as Pandora EMH...it's a brand new experience that is different than before. They could have done better absolutely but I wouldn't have expected perfection for something like this. What would be interesting is did they learn anything from that when Star Wars opens.