This could also be something like corrosion / rust/ gum in the lines/ tubing, and or in the distribution block which is also the piston warning light switch.
My first thought, already mentioned, is to jump on the master and investigate that. The pedal/ pushrod MUST allow the master piston(s) to retract past the ports in the bottom of the master. YOu can see this, maybe with another person, by applying the brakes, and if necessary, pumping them a bit to get pressure up, and then releasing. When they release, watch in the master reservoir and look for both ports to "erupt" a small amount visible up into the fluid. Sometimes these will actually geyser up and splash out of the master, so use rags, etc, to protect.
If you don't have decent pedal on "one pump", and yet it's "hard" when finally pumped up, suspect adjustment. I always turn the wheel and tighten the adjuster until the wheel will not turn. Then back off "some" like maybe a dozen "clicks" and same thing on opposite side. This should be some "even." Until they are worn in some, it is normal for some drag
Also if the drums are excessively worn and / or have been turned oversize, the shoes may not fit well enough. Back in the day, you used an "arcing" machine to match the curvature (radius) of the shoes to oversize drums. In the REALLY old days, you might even shim lining to make it "bigger" to match worn/ turned drums.
This condition causes the shoes to only contact the center area of the shoes. Not only do you not get full shoe contact, and therefore not full braking action, but this overload of the lining overheats it and causes glazing, further reducing effectiveness
