Of course time and distance are going to result is subtle differences in language. You say you are not interested in accents or dialects but in rhythm and phrasing.

People move the accent on certain syllables around. Part of the "rhythm and phrasing". Words come in and out of fashion. As to phrasing. "Bees knees".

I'd say you can't separate those from accents and dialects. Rhythm and phrasing are what helps identify a Canadian accent from the vanilla US dialect.

An English person can tell what part of England someone is from simply by accents which are rhythm and phrasing. Same language.

But imagine listening to Beowulf in the original English and then passing a test on the content. I don't think it could be done. It's always evolving, the past is left behind, and newer brains are trained in newer versions of the language.

Shakespeare is hard to understand unless one has read it first. And yet it's still performed "in the original", but only for the affecionados. Unintelligible otherwise.