I have another POV of this => this is not only a WP/DoK "fault"....
-if you focus WP/DoK => you are focussing a healer with higher armor and with aoe detaunt perma-up, but you are letting a ZE/RP/AM/Shaman (the supossed 2nd healer of the grp) free to ST heal that WP/DoK => these healers have more tools to keep bursted targets alive, also can heal without problems to others allies out of group.
-if you focus ZE/RP/AM/(Shaman) => these healers have lower armor and less survavility tools (only shaman can have some sort of perma aoe detaunt if use the tactic), also the WP/Dok of his grp dont have the right tools to keep bursted targets alive and really cant heal out of group.
I play mostly Dok and when play in a roaming grp with a zealot as second healer y really feel bad cause i cant keep him alive if get focused in situations where he can keep my dok alive...