The D&D I like enforces reality, except when the fantasy takes over.
So, the rope is assigned an AC, Hardness, and hit points. These are based on an "average man" standard. If the PCs are better than that "average man" standard, it is because they are better than the average man. Not because I simply deemed that it was dramatic.
Note, however, that in RCFG, Clint Eastwood's character could take weapon skill ranks in a specific trick, "Part rope with one shot", that would greatly increase his chances of success.
(And, of course, MB didn't have the "greatest marksman in the world" to fall back upon. Remember the MB with splitting an arrow ala Robin Hood? When the Errol Flynn movie was made, they hired a guy to do the stunt. The MB team couldn't reproduce it for love or money, except with an arrow crafted especially for that purpose. However, that doesn't mean that the actual archer hired couldn't do it, and they admitted as much. They also had some film of the guy firing one arrow, and then consistently shooting it out of the sky with another, which I would have thought unlikely at best.)
RC