Aurora is fine on GNB. Even with 2 charges it doesn't heal enough by itself to be an issue for a healer. (it literally only replaces Regen/A. Benefic)
The issue with GNB is Heart of Corundum. The moment the GNB hits half health, they can hit the button and the heal is auto applied to them. Between that, plus two charges of Aurora and I believe its Brutal Shell's shield, GNB has pretty good survivability in a boss fight (W2W can be pretty dicey still). Enough so that I can solo a boss from 90-0 (haven't done 100 yet).
While I would be all for HoC to be tied to the Shell gauge... with the way SE wants the game I don't see it happening. And even then I see issues since Double Down costs 2. Rather, HoC should be more akin to TBN in that there is a set of damage that the GNB has to take first in order for the heal to be applied. This way they don't have a free recitation, they actually have to have the damage be applied first.
I would even suggest to take it a step further, as HoC has a short CD, that if the thresh hold isn't met (aka you use it willy nilly) the recast timer is lengthened. Rewarding good gameplay with said shorter CD.
I dunno. I don't see Aurora as a problem.