God, I don't know where to start with that post. Literally nothing in there is correct, including the use of the words "Aztecs" and "Toltecs." Though, for the sake of convenience, I will use them after a brief explanation.

"Toltec" in Nahuatl (the language of the Mexica, who are erroneously named "the Aztecs") means "artisans," and was use both generically and to describe a semi-mythical forerunner civilization that had existed before the Mexica arrived in the Valley of Mexico in the early 1200's. You see, most of the people in the Valley of Mexico by the time of the Conquest were Nahua, a people who seem to have been migrating into and through Mesoamerica for centuries. The Mexica were one of the last groups to arrive, but it's possible these migrations had begun centuries earlier and had destabilized Teotihuacan, but this is just conjecture. It's known for a fact that Nahua groups migrated as far south as Nicaragua, and there is a moribund language in El Salvador called Pipil that is one of the last relics of this southernmost group of migrants. Obviously, considering how widespread and successful the Nahua were, it wasn't literally millions of people who moved from Northwest Mexico and spread all across Mesoamerica down to Central America, but likely a combination of migration and cultural assimilation that occurred over centuries, similar to what happened with the Proto-Indo Europeans as they spread from the Ponto-Caspian Steppe, but I digress...

Anyway, there's a large ancient city in Northern Mesoamerica known as Tula, or Tollan, which seems to have been the center of a large cultural sphere around the time of the beginning of the Nahua migrations. Because of this, it's assumed that Tula was a Nahua-speaking polity, and it has in fact received the name Tula/Tollan by modern archaeologists because this was the name of the capitol of the mythical Toltecs. Due to the importance of this actual historical city/civilization existing at the same time and place as the later Nahua-described mythical Toltec Civilization, this city is, by convenience, and likely some degree of truth, called Toltec, and so is its associated civilization. But we must disentangle the mythology from the reality. It's possible the later myths described a historical reality in some sense, but it's not really easy to prove any of it, or how much of it.

What this guy seems to be describing as a "religious apocalypse" was the destabilization of the Classic to Postclassic transition, which was influenced by climate change, the Nahua migrations, and numerous other factors. This is also the famous "Maya Collapse" myth in action, as the large cities of the Maya Lowlands were depopulated during this time (though the people just moved around, and the Maya are still around to this day). There is a lot of mythmaking about this era, as you can see from the post you linked, but the reality is more mundane. Civilizations may have fallen, but new ones formed, and the world kept spinning. The Toltecs were certainly not responsible for the collapse either way, as they (both real and mythical) formed their civilization during the Classic to Post-classic boundary, and lasted a few centuries into the Post-Classic (Tula seems to have fallen around the early 1100's). Either way, the Toltecs were likely Nahua like the later Mexica, and most of the other people in Central Mexico during the Postclassic.

Anyway, were the Mexica (Aztecs) religious and cultural reformers? Sure, they made some religious and cultural reforms, like any other people. These reforms were often surprisingly progressive, such as universal male education (though the purpose of this was to raise warriors to serve the state, and nobles and commoners went to different schools). They also, by their own words, went really overboard with human sacrifice. There's a claim that 80,000 people were sacrificed during a single four-day ceremony, though this is likely a ridiculous exaggeration. They likely did sacrifice a lot of people, but we barely have a few hundred skeletons from excavations in Tenochtitlan from what I recall.

Were the Mexica "bad?" What does that even mean? They killed people in the pursuit of territorial expansion. They demanded heavy tribute from the people they conquered. They did terrible things. They also wrote beautiful poetry, insightful philosophy, and creative literature (such as the stories about the Toltecs!). They were masters of architecture and hydrological engineering. They created an amazingly vibrant cuisine that's still important to millions of people to this day. They were complex, like any other people.