Fusing rings in this manner results in a ring with a fusion rating of 'Great', but ends up giving around 4x (!!!) the stats of a ring that is considered by the game to be 'Perfect'.
I have created 'Perfect' Legendary rings myself and now regret the amount of time and money I spent for the materials. Just for clarity, you create 'Perfect' Legendary rings by introducing one new stat in each level of fusion. The Uncommon rings come with 1 stat, so if you add a Gemstone of a different stat into 3 Uncommon rings, you create a 'Perfect' Rare ring. Add another stat that has not been introduced and you create a 'Perfect' ring of the next tier.
However, while mixing stats through each tier results in 'Perfect' Legendary rings, they are by all accounts inferior to 'Great' Legendary rings created using 'pure' Epics.
I have created 'Perfect' Legendary rings myself and now regret the amount of time and money I spent for the materials. Just for clarity, you create 'Perfect' Legendary rings by introducing one new stat in each level of fusion. The Uncommon rings come with 1 stat, so if you add a Gemstone of a different stat into 3 Uncommon rings, you create a 'Perfect' Rare ring. Add another stat that has not been introduced and you create a 'Perfect' ring of the next tier.
However, while mixing stats through each tier results in 'Perfect' Legendary rings, they are by all accounts inferior to 'Great' Legendary rings created using 'pure' Epics.