English definitely has rules.
It’s why you can’t say something like “girl the will boy the paid” to mean “the boy is paying the girl” and have people understand you.
Less vs fewer, though, isn’t really a rule. It’s more an 18th century style guideline some people took too seriously.
One important thing to realize is that different dialects of English have slightly different grammars.
One place where different dialects differ is around negation. Some dialects, like Appalachian English or West Texas English, exhibit ‘negative concord’, where parts of a sentence must agree in negation. For example, “Nobody ain’t doin’ nothing’ wrong”.
One of the most important thing to understanding a sentence is to figure out the dialect of its speaker. You’ll also notice that with sentences with ambiguous terminology like “he ate biscuits” - were they cookies, or something that looked like a scone? Rules are always contextual, based on the variety of the language being spoken.