I still don't quite follow you. with discs there is no spring to pull the piston back. when you hit the brakes it moves the piston until it hits the disc, when you release the pressure the pad and piston pretty much stays where they are, it might get pushed back 1/10 of a mm or so by the rotor.

 

I can't really explain it, but just about every car that I've worked on that had a mushy pedal had either a stuck caliper or slider or a faulty MC or booster.

 

I can/will/do brake with my left foot