The clutch is one of the most basic mechanical systems on the car. Simply put you have a pivot point for your pedal, the arm of the pedal is the lever to give you mechanical advantage and the cable simply transfers the force you apply with your foot. The other end of the cable is attached to the fork which has the TOB captured on it. The fork is a lever as well and transfers the force onto the fingers of the pressure plate. These fingers compress springs that draw the face of the pressure plate away from the clutch itself which disengages the clutch and frees it from the engine rotation.
The only contributing factors to increased stiffness of your pedal are unusual or added resistance to one of these. A higher clamping force pressure plate will have stronger springs and require more force to compress. A kink in the cable can cause it to bind or drag. If the TOB is galled or burred it can cause resistance sliding on the input shaft. I have not seen it but if there is damage to the pedal assembly it could make it harder - with the cable off the pedal would still have resistance. Check each part of the system one at a time and you should find the culprit.
I have seen bent clutch forks on other models that have caused increased pedal or even cause them to stick.
Let us know what you find.
The only contributing factors to increased stiffness of your pedal are unusual or added resistance to one of these. A higher clamping force pressure plate will have stronger springs and require more force to compress. A kink in the cable can cause it to bind or drag. If the TOB is galled or burred it can cause resistance sliding on the input shaft. I have not seen it but if there is damage to the pedal assembly it could make it harder - with the cable off the pedal would still have resistance. Check each part of the system one at a time and you should find the culprit.
I have seen bent clutch forks on other models that have caused increased pedal or even cause them to stick.
Let us know what you find.