Ok so because you mentioned it, Rouse does NOT effect Whispering Dawn. Illumination doesn't effect it either because Rouse only buffs spells, and WD is an ability (not spell). As for aoe heals, you have Emergency Tactics to use on low CD for extra Succor heals if required, the Quickened Aetherflow trait allows AF to be up more often, plus if things get really desperate, there is Disapation as well. Indomitability can be very powerful when used correctly, it's just all about that timing, but SCH isn't that bad with aoe heals.

Fey Union is the strongest MP free regen in the game (at 480 potency) and you would benefit using this far more than spamming Physick (400 potency), so it's definitely not the same or weaker. You can also stop the fairy at any time during Union should you need them to do something else, so you have complete freedom in this regard.