I am dubious this actually happened. It's like you took every hyperbolic argument against AD&D and expect us to believe literally every single player in your group was legit making those hyperbolic arguments, and making them in a specific order that just so happens to cover all of those arguments in the most convenient way. Presumably if your players were not familiar with AD&D, they wouldn't make half of those statements unprompted, because they require a knowledge of how the system worked. And others just don't make sense from an organic sense, like your first example.
Like what? Do you have an example of where it's confusing is a monster wore armor or not? It as pretty clearly spelled out. Take the orc for example. It told you what the natural AC is in parentheses. That's how it was handled, as described in the MM.
ARMOR CLASS is the general protection worn by humans and humanoids, protection due to physical structure or magical nature, or difficulty in hitting due to speed, reflexes, etc. Humans and humanoids of roughly man-size that wear armor will have an unarmored rating in parentheses.
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