Haven't seriously try out healing in release, did a bit of healing in beta...which sucks.
Take wow for example, healing take more than simply clicking non stop to be efficient (except for LK where 1 button spamming ftw...so stupid) The reason your healer failing might not have anything to do with add on at all...its just they simply suck and dont know how to play their class properly.
Add on might make things less challenging to a certain extent but healing manually in a OP group is just messy...it is doable but just not efficient and cant make use of the full capacity of the healer because we spent too much time clicking on targets