When I had the stock MC my symptoms were 3/4 throw nothing, then grab. I also had a booster which leaked (engine would almost die with foot on brake at a stoplight) After I switched to the larger ZX MC, installed a used booster and later played around with new pads and such it worsened to no significant grab. The brakes were applying, but weakly, and holding the pedal to the floor would only gradually slow it down. That's when I finally searched and found out about the reaction disk.
My system was stock though, except for the ZX master cylinder and some fancier pads and shoes.
There are some other cases that cause similar symptoms though. For example, from what I've read the guys that install the Toyota 4x4 calipers accidentally upside down and on the wrong sides (can't get all the air out of the lines) usually have some similar pedal problems. Once they switch sides and get the bleeders at the proper altitude they can get rid of the air.