Now I'll agree with many stuff on here, mainly on the tonal issues this episode presented. These points I'll present are ones I believe on the other hand differently.
1. Alright, first point I want to contest is your point on Fancy Pants. You assert that Fancy Pants is ooc because he reacted hastily and harshly to how things have happened at the Equestrian Summit among other things.
Here's one issue I'm arguing against, why is Fancy Pants asking Princess Twilight to see if she'll grant him VIP passes for himself and whomever he chooses a bad thing? Especially considering how he reacted to Spike's refusal in Twilight's name with an appeased attitude despite not getting what he wanted and that Twilight is the one heading the summit and was the one he scheduled to meet with to discuss on getting those passes.
His anger is also more understandable in the form of these points:
A. It was he who ordered the the trees to be trimmed but yet finds that not only they weren't but the reason why his order was disobeyed was according to the tree cutter Twilight's orders them not to have them cut down. This is further built upon with a possible implication that he may have ordered the water pipe to be fixed only for it to be disobeyed in favor of Twilight's orders as well.
B. Fancy Pants: "I'll not let Princess Twilight give Canterlot a bad name in the eyes of Equestria! Come on, everypony! Let's go give her a piece of our minds!"
Here, we're presented his motivation and reason to be angry, his home city's name is degraded by Twilight's poor decisions in front of a summit where representatives from across Equestria are seeing right before their eyes. How do you think those representatives are going to look at Canterlot that had a water pipe burst, trees falling down, and their meeting hall drenched in water from the water pipe on the day of the meeting? Not very highly I'm afraid. To make matters more personal for him, because his orders were disobeyed to have them fixed only for Twilight to say nope don't fix them, how do you think anyone's going to react knowing that not only were their orders superseded by someone but that person's decisions led to a disaster for everyone involved? Understandably peeved. That's not including whatever is going on behind the scenes with the upper class in Equestria that again are not going to look Canterlot favorably after what had happened and thus he's likely going to suffer a hit to his reputation and especially the city he represents unfairly.
C. He finds that there were many ponies who were also not pleased with Twilight's decisions as well who are just as ticked at their own results and how the meeting turned out. Thus of course he'll be leading an angry mob of ponies who share their disappointment in Twilight's decision making that has caused many bad outcomes on that day, even if he didn't called for it, I'm sure many would follow him to the tower regardless.
2. On another matter, your criticism on the ponies meeting solely with Twilight instead of the other princesses suffers a couple of issues in my opinion in the form of:
A. We have no proof other than Cadance later in the day of the Princesses being available. For all we know, Luna and Celestia are probably working their butts off handling another group of ponies or other things to keep the delegation and day well at Canterlot and Equestria. To assume that Luna and Celestia should be at fault because they're not there in the episode after the prologue is to me unfair for them. None of them received any advance warning that their meeting is called off so why should they change their schedule to meet with someone else instead?
Cadance has a bigger fault for it because she actually was the one who not only tells her sister in law to sleep for the day, but rather than tell Spike what he should do should any of Twilight's delegations come or even tell the meetings to be postponed at a later time she doesn't do any of that, and to a lesser degree, Twilight because she should've planned better than to spend three whole days without sleep dealing with the meeting.
B. Why should they not expect their princesses to give them answers they seek in their meeting? Not only is it shown to be a responsibility for the princesses to do but it is something they've come to expect with good results after how long Celestia has been in charge handling those delegates and how Twilight has handled with various situations in Ponyville and Equestria as well.
3. About the issue with the two worker ponies who were busy working with important assignments, they were explicitly ordered from Spike representing Twilight who had wanted to keep things quiet for Twilight under Cadance's orders to stop their work. You can critique about how they should've thought with initiative like Spike did when put on his own, but considering how they were ordered by Twilight to not to do their work for at least a few hours. A thing is that when you're ordered by your leader to not do this at their request, you probably have to obey or so lest you face discipline for disobeying orders most likely even if you believe it is the most idiotic order imagined.
4. I believe he did closed the windows considering we see Spike through a closed window looking to see the polo (one thing I know I'll need to edit in my review) playing ponies that were actually shown disturbing Twilight's Sleep as she was moving annoyed by the noise. Thus he had every right to act on that situation. As for asking Celestia for a sound proof barrier, that's assuming such a thing exists, she actually knows doing such a spell, and she wasn't busy elsewhere that he can reach her.
Other than that, many of your thoughts in your excellent review I agree with on many points. This is merely something that I wanted to add below this comment section with what I consider wrong in the review. It is my personal opinion of course.