Using S rank Jewel of non-main stat

The stats of the rings in the data don't match their stats in the Update Notes. They're higher. I believe this is why most every ring the bunny crafts is "below average", and fusing them improves their stats. The bunny gives artificial stats based on the same source as the update notes, but fusing gives you a random clean item based on the data.

I came to the same conclusion. Although the deviation of stats seems to be greater from fusing than from crafting.

Huh, I wonder if that means fusing A rank Rings together would give better results than making S rank jewels? would be easier too.

It's definitely a possibility. Of the 3 Keen S rings I've actually succeeded in crafting, all of them have been underaverage ranging from 8 to 9 m.atk, although the attack always seems to be average or above.