Riddle of Earths' change was unnecessary.
Removing the charges and instead making it a single 120s cooldown that gives a HoT is just baaaaaaad. Why in the world would I need an overall 500 potency HoT when healers should already be healing that damage I'm taking anyways? The way this is, I'm likely only ever going to use it on a raidwide or a mechanic where I'm specifically targeted, which, again, makes the HoT kinda pointless because the healers should be healing everyone necessary anyways.
If you wanted to improve its "ease of use" as you claim, you should have just made it a flat 10 second damage reduction. No falling off when you use GCDs or get hit or anything. Make it a single charge if you must, but don't make it 120s, that's atrocious, make it 30 seconds like it is was.