As far as the spring pressure, different cars are different. But here's a few dumb guesses if yours is getting stiffer than it used to be...

You filled the fluid - when was the last time you changed it? You should flush it every 2 years so its fresh. Old fluid is corrosive because it has absorbed moisture from the air.

How are the pivot bushings & pins & clevises of the pedal itself? Maybe they're getting dried up & need some grease.

Check out the rubber hose at the slave cylinder. Is it kinked or damaged in any way? You'd expect it to leak if its messed up, but maybe its collapsing inside? (I don't really know how likely this is, I'm just guessing.)