My personal theory is that the SR line is the largest contributor to RSR wait times. People who disagree with this will claim that they are just taking places in a partially filled car and, thus, not increasing waiting times. I disagree; using the SR line to fill a car has become the norm for CMs loading the rides, but if you think about it, loading the cars to full capacity can be done through the regular line. The CMs load and call for "party of 2," or "party of 3," etc. This is standard for SM, BTMRR, Pirates, and even Indy, which has a SR, but I notice the CMs always check the front of the line for smaller parties.
If the SR were eliminated, it would reduce the lines by deterring some individuals or families from riding multiple times in one day just because SR is easier than getting a FP or shorter than stand-by.