Dissipation's primary benefits are the immediate three aetherize stacks, which are very useful, and the +20% healing buff that applies to your Physick, Adloquium, and Succor (and only those skills). The detriments to the ability is the loss of the fairy which can be large if you're using Eos unless her abilities are all on cooldown, or limited mostly to just Embrace if using Selene, as well as both the expensive mana cost for resummoning the fairy and often the use of Swiftcast to do it. And those last bits are it's real problem, because the skill requires a sense of commitment to it. You can earn the mana for resummoning the fairy by using some of the stacks gained with energy drain, or you can accept the 1800 mana cost. You can then decide whether you want to resummon the fairy with a hard-cast (recommended if the boss is about to jump away for a while), or burn your swiftcast timer and lock yourself out of swiftcast for its cooldown, limiting your res and recovery potential. You may also decide to not resummon the fairy, in which case you are the healing equivalent to a NIN that doesn't use Huton or a MCH that forgets Hot Shot.
Most of this would be remedied simply by having the fairy return after the duration without having to be resummoned. Three aetherize stacks on demand is a powerful benefit, especially coupled with a Divine Seal effect that further stacks on top of actual Divine Seal (Largesse), but the enhancement comes at a cost you have to pay not in the present but half a minute in the future, and unless you're confident in what the situation will be like then you may have reservations about consigning your Swiftcast or mana cost to it. And make no mistake, it is actually a useful ability, but even if the cost is something you're willing to pay there's something thematically off about a SCH getting rid of its unique class trait for a buff that puts you at a disadvantage later unless addressed.
