Gene could explain why. that was that lower levels heals better with 100% ring (unclear why) then higher levels. Thats why Gene has changed all the lvl 25 rings of 100% or less to 66%.
You can find 100% healing rings from lvl 28 now. So now you have to level up for a good ring.
Edit: The bugs of the 100% healing rings are removed. So Gene had no reason to keep him at lvl 28. All rings are put back. So you can be 100% healing rings again like lvl 6.