It's not only the fact that with rope drop, your wait time isn't using up valuable park time. With rope drop, the big benefit is how long you end up waiting for your 2nd, 3rd, 4th rides, etc.
If you are smart at navigating a park, RD saves you a lot more time than just that first ride.
Example: Magic Kingdom. If you rope drop 7DMT and are among the first to ride, you might wait 5-10 mins, finishing up before official park opening time even begins. Then you could move to Space Mountain and ride with a minimal 5-10 minute wait, because all the people arriving at official opening time are headed to Fantasyland. Then you could Ride Buzz around 9:30 or so, again probably 5-15 min wait. Then squeeze in a couple more rides (Tomorrowland Speedway, Dumbo, Barnstormer, etc.) before the crowds start to get long everywhere around 10am or so, at which point you can start having your fastpasses lined up for things like Peter Pan, Big Thunder, etc. (all of which would have >45-60 min waits).
Versus: Arriving at official park open. Stuck in security/entrance for 15+ minutes. By the time you make it back to 7DMT, the line is over an hour. By the time you've waited through that and completed one ride, the waits at all the other big rides (Space Mountain, Splash, etc) are an hour long.
So that 45-60 minutes you've arrived early for rope drop saves you several hours of waiting in line during park hours to accomplish the same itinerary.
The above example could be extrapolated to Animal Kingdom, though if you have to arrive 60-90 mins early, the returns might be a little diminished.