I'm aware that the Roman ranks never really scaled with modern-day ranks, I basically used the term for lack of a better one really. When I said "make a comparison chart", it was strictly in the context of how the Roman Army itself evolved on its own terms: Who commanded a Legion at any given time (Legatus Legionis, Praefectus Legionis, Dux, Comes, etc.), a Cohort (Centurion, Centenarius, etc.), rather than say, "Oh, a Centurion is some strange hybrid of a Captain and a NCO at the same time due to their responsibilities". Useful for fiction, but without context, it's very misleading and wrong.
However, a thought did occur to me. Would it make sense/ be logical to organize the chain of command within the Roman Legion by Command Level? (e.x Arrange Legates, Tribunes, and Prefects as "Legionary-Grade Officers"; Centurions, Options, and Signifers as "Cohort-Grade Officers", and so forth as you get down to the smaller levels like Vexillations and such?
I guess the reason I began this topic in the first place was because I wanted some more information on the difference between the "New Model Legions" Diocletian and Constantine made, versus the Old Model Legions of the Late Empire, since I find many referencing talking about the two, and wanted to compare them both with the Principate Era Legion... hence wanting to make that Evolution chart.
Apologies if this response came out rather disjointed...