I understand your observation. I mostly agree.
Mine seems to be about right. After owning 20+ motorcycles, and working on many hundreds, as a second job for many years at a dealership, I think there is a difference between models and mostly adjustable by the outer sleeve of the cable.
I think the springs are a pretty uniform product across a particular model.
Also I have "fixed" stiff/sluggish cables with lube.
Not recommended, but an option:
If really demanding by someone, you can cut 1 mm off the end of the spring a few times and it will "adjust" the tension, but it changes both ways. I don't like it, but, back in the 80's, we did some on a few mods to a few motocross bikes to reduce response.
With fuel injection, I think it makes things a bit touchy.
Long ago when cables were $5 it was so easy to just fix it with a new cable.
Now with prices $30-50 they are more reliable.
The return spring on my rocket is strong but even.
The nice thing about the TM is that it is infinitely adjustable for pressure against the tension.
I only use the TM for cruise on the highway.
I don't do it around town. I like the control that the Rocket already has.