Delta hired everyone that made the score- don't try to make it into some conspiracy because it's not. . A good number of lifers did fill out applications attempting to not be lifers, but a good many did not. The 65-85% pass rate were the first couple days. However, that like most any large scale thing will be honed as it ebbs and flows and finally creates an average. The overall average thus far for the rather senior portion of the group was 30%.
It's logical to assume that the average pass rate will go up as you get into the main cadre of guys that want out but have not had a shot due to the stagnation the last few years. Were you really saying that they intentionally only hired 30%? If so... take a step back. It is a scored interview process with set standards. Everyone, SSP and off the street, is held to the same standard on day 1. Everyone that makes the score gets the offer.