It's like that joke about spherical cows in a vaccume.
No, the conditions of life are constantly shifting, particularly in language. Since language is about standardised communication, the rules are constantly shifting as people change them without realising. But by the same logic, they must remain uniform. This is why study of language can be a full time job and recognised branch of science. So yeah, it's both what people use and what they are supposed to use.
Everyone gets taught the same things because they exist to be a common starting point and enable communication. variations are inevitable but the standard must exist. Where you go from there is up to you. So long as it's coherent, and legible, it will be fine. And thats what proofreaders are for, headache absorbers
Besides. Mess ups can add character