I have swapped springs on the front struts of a T4R and spring rating does make a slight difference. The T4R has a lot of brake dive when stock. Old Man Emu struts and springs made a big difference. Almost too stiff for my minimal added weight. I tried a lighter Old Man Emu spring and the ride improved only slightly. The brake dive returned but it was minimal. The spring swap wasn’t worth effort or expense. On the T4R I’d say that the new AT tires vs stock P made the biggest difference in increased road feel.
I have also swapped to heavy rear Old Man Emu from lights on the Jeep. I noticed no difference in ride quality, just a 1/2” higher ride height.
The only way a spring changes the ride is if it changes the ride height. Changing the ride height changes how the shock behaves with regard to its travel bias.