Help! I'm having problem healing GNB mass pull.

[Semirhage]

That's indeed how it works but the problem is that nothing in any of the tooltips makes this connection obvious.
And the fact that Fey Illumination applies a buff to all party members for healing done instead of healing received doesn't make it any easier to make this connection. Any of the buffs, like Temperance, Fey Illumination and Dissipation could easily be changed to affect oGCDs by simply applying a double buff to the party that increases healing received.
The problem is still that none of the tooltips make it obvious what is affected and why.

Updating healers so their abilities make sense? Why on earth would that ever happen?

[Rilifane]

Updating healers so their abilities make sense? Why on earth would that ever happen?

They'll probably update tooltips from MNK etc. so they make sense and completely forget about the role nobody cares about and that doesn't really exist anyway.
I'm a giant pile of salt.