Plot hole: There is no reason at all why, being targeted by a few arrows by unseen enemies - a fire suppressed already by the salvo of their own archers - the Rourans would turn around their heavy siege equipment, away from the bulk of the enemy forces, and fire it, hurling a single heavy stone to the middle of nowhere when they have the whole rest of the army who could storm the rock the supposed enemy commandos hide behind, or the archers who could keep shooting - again, they proved to be completely successful. It also makes no sense that the all-powerful witch who made the warriors flee managed to do any of this, 'sneaking' by horse in the middle of the steppe.
Suggested correction: Mulan used the helmets of the fallen warriors to make it appear that a large force has flanked Rourans. Rourans didn't expect this new "force" and knew nothing about it. They didn't know its size. And while their original target seemed harmless, this new "force" was killing Rourans. Fear and death were the reasons. What you see in this scene is an enactment of one of Sun Tzu's famous quotes: "All warfare is based on deception. [...] Attack him where he is unprepared, appear where you are not expected."
What we see in the scene is laughable, and not because of the idea, which surely is based on the profound strategic motto you mentioned and we find in many folkloric tales in other cultures as well; what we actually see in the movie, is that she grabbed a couple helmets lining them up on a rock, and she shot a few arrows. Then she stops shooting, and we see helmets knocked down in their full view. The movie truly surpassed itself in showing it in the most phony way; had they shown her shooting from behind the rock responding to their fire, or the helmets not falling, or them just shooting at mist, terrified, it would have maybe worked. It's an enormous overreaction. That and, under no circumstance trebuchets are used that way anyway. And she did all this setup unseen, again.
In response to death, nothing is an enormous overreaction. Something or someone was killing them. They wanted to kill it, and they didn't have time for Facebook's famous brand of pseudo-myth-busting. What if they knew it was one girl shooting at them? They'd still have done the same. Being killed is a very personal matter.
Plot hole: Enola and Tewkesbury make an unpremeditated decision to visit the Basilwether estate. This decision was made on the spur of the moment, and no-one knew about it. but when they arrive, Linthorn, who is supposed to be in London looking for Tewkesbury, is waiting in ambush to kill them. (01:32:45 - 01:34:31)
Suggested correction: Linthorn saw them in London. He travelled back to the Basilweather estate, and waited for them to slowly make their way there.
Enola and the young Tewkesbury were in London two weeks prior to Enola's forced enrollment in a boarding school where she was supposed to spend her next few years! Furthermore, there is no evidence of Linthorn having seen them.
Plot hole: The whole premise of the movie is that history would write off the existence of the Ghostbusters after the events of the first movie. In that movie there was prolonged large scale destruction in the heart of a city with millions of inhabitants. It's simply impossible that people would forget or dismiss it. And that's if we do not even begin to assume that the second one happened, even if the director said it did; nothing in his movie shows that, and for a good reason (Statue of Liberty, anyone?).
Suggested correction: There's nothing in the movie to indicate that people in general have "forgotten" or "dismissed" the existence of the Ghostbusters, nor is that the "whole premise" of the movie. The fact the teacher is a fanboy and that the characters literally watch old news-clips and commercials for the Ghostbusters kind of goes against this. People simply just stopped talking about them because they did their jobs too well and went out of business 30 years prior... they were no longer relevant. I mean, if you want a real-world-analogue, just look at 9/11. It was a massive, generation-defining event, and yet outside of brief memorials once a year (which honestly, fewer and fewer people seem to pay attention to every year), people basically don't talk about it at all anymore. The only characters in the movie that don't believe in ghosts/the Ghostbusters at first are the kids. And their mother has been purposely sheltering them because she hates their grandfather-a Ghostbuster. So it makes sense they wouldn't necessarily know about them.
9/11 was a different kind of event; it didn't have 4 easy to remember heroes who already were on magazines covers all over the world and while it certainly dropped off the radar in many ways, some consequences in the long term have been permanent and it is in the history books. Here the world had proof that there are other dimensions, the dead, etc, and years later the Ghostbusters are relegated to a few youtube videos with a few thousand views (that with Peter supposedly teaching advertising and promotion, even). I didn't mention the kids, although the movie itself knows it's absurd that Podcast does not know anything about it and there's a joke about it. I understand if someone makes a point about the movie taking an ample creative license for the sake of not having to deal with 'realistic' implications of its comedic prequels since it wouldn't service the kind of story it wants to tell here, but I am surprised you say that the Ghostbusters here are not forgotten or dismissed. Somehow they are so fringe that not even the conspiracy theory guy knows about them, and the teacher knows because they are a childhood memory.
Like Ray tells a young Jason Reitman in Ghostbusters II, "Well some people have trouble believing in the paranormal." The public would have even less of a reason to believe in or think about the Ghostbusters since there were no Ghost sightings in thirty years. Not to mention the fact that men walked on the moon six times between 1969 and 1972 and astronauts were viewed as heroes, but we haven't visited the moon in fifty years, and astronauts are no longer regarded as heroes.
We keep conducting research in the field sending people in space when and where necessary and people are well aware that astronauts exist, even if they declined in popularity. It's not random obscure knowledge you can get only if you are looking specifically for it on some Youtube channel that a science nut and a conspiration theorist never heard of before. And we are again comparing something that does not have the same impact it would have to learn that dead people still walk (so to speak) the Earth. BTW, I am not sure (but I could be wrong here and please correct me) that the movie says that there have been 'no' ghost sightings at all; Ray said that they received less calls, not enough to pay their bills, not that ghosts disappeared entirely. It's just that in the Ghostbusters universe, people are kinda jaded about everything, which worked when the movies were comedies and you could say it was obvious paradox and satire that they would save the planet and still get sued once they weren't relevant anymore.
Plot hole: After the incident in Chemistry class, Adam was taken to the hospital where he was diagnosed with schizophrenia. Next, Adam found out that he was expelled from school. What happened during Chemistry class was attributed to Adam's "first psychotic break" - which would fall under a medical condition for which Adam could not have prevented or controlled. The Department Of Education has laws protecting students like Adam (Individuals with Disabilities Education Act or IDEA, enacted in 1975), and the school is required to meet the child's / student's needs. An Individual Education Program (IEP) should have been prepared for Adam by his school, so the expulsion served to further the plot. (00:06:00 - 00:06:30)
Plot hole: Social Services requires even emergency placements to be approved. A child (9-year-old Tulsa) who had never seen her father (but "just knew" the man in the photo with her mother was her biological father) would not be allowed to stay with a man who did not even know he had a daughter. Social Services would not assume the child was correct or leave the child with a non-approved "stranger." Tommy's apartment - trashed and scattered with beer cans and bottles of alcohol - would be a big red flag. (00:03:55 - 00:12:00)