One can press the hammer back to take the effect of the hammer spring, and the friction between the seer and hammer out of the equation. Then work the decocker with only the decocker spring tension. That would tell you if the hammer spring contributes much to the resistance.
I noticed that decocker springs cost $2 online at Cajun Gun works, so you could buy a couple and experiment with relaxing them a bit.
https://cajungunworks.com/product/62-decocker-lever-spring/I would guess that the notch on the hammer that holds it in the cocked position will smooth out with wear, because as the gun is decocked, you basically have two metal edges sliding past each other. (I did not buy mine new, so I don't know how it was then)
Incidentally, an older CZ handgun was notorious for the decocker failing with wear and causing accidental discharge. It is possible that for that reason, more recent models got a much stronger mechanism to prevent that from happening. In other words, although one can probably lighten the decocker spring, it might not be safe to do so...