To be honest,
I'm not sure how or why the Kyosho springs (and big bore shocks for that matter) are or have become the benchmark for many racers/Mfg.'s. The 1/10th springs are for sure some of the most expensive springs I've bought (cost more than their 1/8th springs). Only thing I can think of as to why, in part, is that the springs aren't made by Kyosho directly. X-gear makes them for Kyosho and is likely one of the few things Kyosho doesn't make for themselves. So I'm guessing that's part of the why they cost so much. As for the the quality or why the quality is so much better, I don't have a clue.
In a pinch if I didn't have the Kyosho springs I wanted/needed on hand,
I have used all of the afore mentioned above at one point or another. It got me by for that time I needed them. I think the closest ones I've found to the Kyosho are the Losi low freq. springs. Don't know what's all that different with them over the regular Losi springs, but the low freq. "felt" close to the Kyosho's. Are the differences between springs really enough to tell? I know I don't or haven't always been able to, but I do tend to revert back to Kyosho springs when I have the ones I need (which now I have all of them. Lol) and don't really use all the rest I have in the box.