Battle-line rotation during the combat

[Mitra]

Over and over again we read words from that time that strike us as common sense and good wisdom

Obviously, no man want real blood for simulate real battle, but this is why the sources interpretation it is a necessary starting.

that in itself suggests that they thought pretty much like we do.

You are free to think like you prefer, but exist studies about warfare, economy, sociology, etc which don't agreed with this affirmation. Roman world it is a pre-modern world with pre-modern scale of values.