To add to your post - The few hundred Spanish soldiers were not invulnerable in battle. Aztec weaponry was strong enough to pierce the armor the Spanish wore. The decisive advantage was the thousands of Indian allies.
“European disease” turned out not to be the biggest culprit in the native die off at that time. A few years ago the pathogen was ID’d as a hantavirus causing Hemorrhagic fever which is native to the New World. The same pathogen had caused a population crash before.
In New England the first colonists saw many native villages depopulated because of disease.
I forgot to add that Cortes did have a few canons that were taken from his ships that he had burnt along the coast. Imagine landing in a strange land, marching inland, and burning your ships behind you so your men would have less temptation to mutiny. Talk about commitment and courage!