The cloak in question doesn't have +magic, only Int. Which means it doesn't affect things like the Burn to Death DoT. Your top damage dealer is irrelevant; what matter is how much an upgrade affects total damage done, and all else being equal, Int is usually less valuable because it affects less of the total damage sources. But this cloak has a ton of Int, so it might come out ahead anyway, especially when factoring in Will of the Sublime as pointed out above.