I've been thinking this same concept and I like this. This is exactly the sort of thing SCH needs to bring it's AOE healing up to par with WHM/AST. For example in SusEx, whenever he casts his triple hit raid AOE, deploying Adloquium/Excogitation beforehand to soak and heal the first two hits, while using Emergency Tactics and Succor for the last hit will bring SCH to where WHM is with Cure III.

I don't think this is at all overpowered due to the long cooldown of Deployment Tactics (120s). Even if you manage to get a crazy powerful shield with a crit Galvanization from Adloquium to spread--that's a cool story bro--but adding the Galv and the Excog together defeat each other's purpose: one allows you not to take damage, the other heals you. Since they're both 30s in duration, a strong shield will likely just nullify the need for Excog on any player who isn't the main tank anyway.

(I also agree Excogitation should heal at the end of its duration regardless--a healer should not be wasting a heal especially when that heal has a special non-MP cost.)