Blizzard has addressed the concerns raised about trinkets in Dragonflight Season 3, and has announced modifications that will be made to both 
Nymue’s Unraveling Spindle and 
Rashok’s Molten Heart.
(Source)
Ultimately, the feedback received suggests that this trinket does not provide an enjoyable experience in its current state and feels like an underwhelming damage trinket with a lackluster Mastery buff
We appreciate the feedback and the data from testing. There will be several adjustments in the upcoming update:
- The channeling time has been reduced to 3 seconds, along with corresponding modifications to the damage and Mastery values
- The duration of the Mastery buff has been increased to 18 seconds
- The Mastery has been boosted by approximately 40%, even after accounting for the changes in duration and channeling time. The current value on the PTR is actually a bug that accounts for the lost rotation time
- The damage per second channeled has also been slightly increased
- The bonus damage to rooted targets has been raised to 50%
(Source)
It appears that there is a scarcity of effective healing trinkets in this raid tier. It seems like we will continue to rely on the Rashok’s trinket for some time.
Healing trinkets will undergo adjustments in the upcoming weeks.
Rashok’s Molten Heart has provided more power than intended, and will require some changes in addition to the reduction in mana restoration.
