Um, the parking brake has nothing to do with the rear pads. The parking brake is a separate set of shoes inside the hub of the rotor. I'm not sure how they explained the 50%. If this is the original set of brakes and the rears go before the fronts (fronts being what about 75% of the stopping resistance) I'd suspect a sticking caliper.
As for not feeling a difference with a fluid flush that's a good thing. By the time you can tell something is bad it's kind of too late. That's why they call it "preventative maintenance"
2010 Legacy 3.6R (Mine) 2013 Outback Premium (Wifes)
2001 Outback (Son), 2001 Forester S (Daughter)
1999 Miata (my summer ride)