Agree. All theories and hypotheses that had prevailed from the moment the content of the movie became known, until it came out, have been put under strong doubt after the discovery of the station hall in Zephyr Heights and the fact that the various pony tribes that were to be in conflict with each other, simply not knowing that the loss of magic was equally widely distributed. Then it had emerged that the ponies seemed to have “forgotten” so much, that Argyle had to work on finding out about the past - and it is possible that the “Journal of Friendship” book that Twilight had left behind was untouched so Argyle could find it.
Maybe because an alicorn had made the book. The three crystals, which were magical all the time, were probably untouched because an alicorn had made them and put a powerful spell in them. All magic - active magic - was gone. But probably not those with high magical power. Perhaps the Crystal City is intact as one of the 12 states in Equestria. As expected, the magic had disappeared, with the clear exception of internal and inactive magic such as ponies can hold objects with their hooves. With one exception - and perhaps two if Argyle had based his research on the Journal of Friendship which has not been shown in the movie, perhaps hidden somewhere in the lighthouse. Only from there could he find out the most intricate details about the Mane 6 and their adventures.
There are lots of hints in the movie that show that something dark and ominous is coming, it was a big shock to discover that the time between the disappearance of magic and the movie is too short, down to just two generations, and according to Izzy as Zipp, it happened without notice. Grogar`s Bewitching bell and the Memory Stone were observed (perhaps the spring after Twilight Sparkle suggests that she can return, if only to help Sunny when she becomes a permanent alicorn?) in the lighthouse, and there are indications that Argyle turned out to have secrets, may have died prematurely due to his research. The bell is ominous.
We know very little about Grogar. We do not know how Gusty the Great managed to defeat and banish a tyrant who was so powerful that he could smash “a thousand armies”, only that the theft of the bell was part of her plan to get rid of him. But the bell itself was unbelievably strong, Twilight had to extract harmony magic from three groups - 18 element bears - and the Terror Trio was combined as strong as Celestia or more, “three alicorns strength” - to take all the magic out of it. A weak magician can not handle something so powerful, so Grogar had to be far stronger than we know. Maybe on a par with a full-grown alicorn. And it’s a fanon theory that Grogar may have created Discord as his masterpiece among the monsters.
But that does not mean that Grogar is the only candidate on the list of the suspects, the fake “harmony knights” from the IDW S10 may have been guilty of similar crimes - the abyssinians had lost their magic, the diamond dogs lost their community, the zebras and others in Farasi may have lost their history, the ornithians may have lost their charity (probably due to malfunctioning element three) - all this has happened to the Ponykind in the G5. We do not know what happened to the fake “knights”, because the last issue has not come out. If Twilight sentenced them to eternal stay in Tartarus, they could escape from there and take their revenge on her. But there are no hints about them in the movie, possibly because the idea of many element trees was poorly received by the fans.
If it’s Grogar, Equus may be safe - yet. For fear feeds his magic, and this seems to be just one of several sources for his magic - hopelessness can be included here. The ponies may have “fed” him with fear magic for probably a hundred moons or more, as these lived in fear of each other. Fear is something that was very pervasive as a strong common thread in the movie, only Sunny and Izzy were fearless in the beginning while the pegasi has its natural aggressiveness. If it had been going on for so long, without the bell being activated - it meant that Grogar might not be in the same dimension as the ponies.
It’s a theory that has never been ruled out, that Gusty the Great banished Grogar into the limbo, just like in the G1 - along with his city of Tambleon. Possibly the banishment could become permanent by removing the bell and then smashing the larger and older bell. But it could mean that the barrier between Tambledon and Equus is weakening, so Grogar can use his magic to manipulate events to create fear, while destroying the worst threat to his return. And maybe the bell played a role in his plan.
By ascending as an alicorn, uniting the first leaders among the ponies (three out of 12 states, she has only just started - and if Grogar is involved, non-ponies can also be affected, so she must reach out to them) and returned the magic to the Ponykind has Sunny stopped the feeding to Grogar. The song that Equestria may be in danger may be more real than we think. But it may mean that she only postponed the inevitable.
We do not know what had happened, because if the ponies were exposed to memory erasure spells just as they lost their magic, it meant that they could not remember the horrible moment when Equestria collapsed, and thus had only bits and pieces of vague memories when the gaps in their memory filled, which can easily put them in conflict with others when they need scapegoats for the loss of something they do not understand.
But Canterlot seemed to have disappeared even though it is next door to Zephyr Heights, where the pegasi does not seem to know that it was an ancient city of great historical value nearby. The whole valley with Ponyville is completely absent in the movie. From the very beginning, the Everfree forest is a mystery, in the first seasons it was first thought that it was non-magical where monsters were trapped from the rest of Equestria as a kind of animal sanctuary. But in recent seasons it was learned that the forests are magical, which had to be kept in check by either the ponies or the harmony tree as there is malicious and dark magic there, with unusually many chimera monsters there. Discord claimed his ex-girlfriend Cosmos created Everfree, but few believe him. With good reason because his story is full of big holes that one can run a jumbo jet through.
According to my headcanon, it is possible that this was where Grogar had his capital - Tambledon - in the valley, which formed the core of an area that later became Middle Equestria. Gusty the Great and his army, which probably did not only consist of unicorn warriors, had gone there long before the modern Equestria was formed. In the IDW comics we learned that the griffons had claimed the area as “undiscovered” or “undeclared” land subject to their authority. The ponies had refused to claim the valley until the great frost forced them to flee, and colonize Middle Equestria. The griffons thus sold them land rights. Something is very special with this particular valley where most of the G4 happened.
Which has now “disappeared” from the G5. We do not know. The absence of this in the movie, where only a reconstructed map from probably the pre-S8 Equestria is seen, is very telling. What happened to the Ponykind probably has its source in this valley.