Yeah, I know what I think has happened because I once did the same...
If the release bearing gearbox internals are the same as mine, you can slide out the shaft that engages with the release forks. But you can slide it back in, in a different position. So the bit that engages with the cable will be in the wrong place to get maximum leverage. I think that makes sense?
The way it's supposed to be- is when the release bearing is just resting on the pressure plate springs (fins), the lever that the cable hooks onto should be just below centre. So at half clutch, the lever is at 90 degrees to the cable- and at full clutch just above centre. So easy to show, but difficult to explain! If that's ok, then it'll be either the cable (wrong) or the pedal end.
My first thought was pedal box, but you say that's ok.