Diaphragm spring clutches - which are the most common these days - do tend to get heavier to operate as the friction lining wears. This is because, when new, the dish shaped diaphragm is almost flat at rest so takes little force to depress. As the linings wear the diaphragm becomes more dished when at rest and takes more effort to "straighten out". It's difficult to ascertain whether a clutch is "heavy" or not unless you're driving a number of different examples of any given car because the clutch wears very slowly so, if you're the driver of just that vehicle, you get used to it getting slowly heavier as the years roll by. It's pointless to try comparing it with another make or model of vehicle as clutches do tend to vary in how much effort it takes to operate - For instance, my old diesel SEAT had a secondary "helper" spring on the clutch pedal which, due to an "over centre" operating mechanism, came into operation once the pedal had been depressed a wee bit, helped you to push the pedal down. A clever idea but, if you were dismantling the pedal cluster - as I had to do to weld up a crack in the pedal - it was a pure sod to get back into place as it was a very strong spring which had to be partially depressed to fit. The point is that without the "helper" spring the pedal was excessively heavy to depress which, had the spring broken or malfunctioned, you'd be tempted to diagnose as a worn driven plate or some other internal clutch part and set about taking the gearbox out to check! Because this slave cylinder problem is so common on our particular model with the wee FIRE engines I'd try a slave cylinder almost without giving it too much thought.
