If you outgear the content that much, then perhaps you don't need the TBN since you aren't taking enough damage to need it. Presumbly you'll figure out that you are overgeared when it doesn't break and stop using it.

Camouflage is also an optional, for-fun buff since GNB has the essential cooldowns already as well. Perhaps it will act as a light cooldown in big pulls.

There are only so many ways they can diversify a mitigation cooldown. If Dark Mind didn't mitigate just magic then it would be a clone of either Rampart or Shadow Wall.

It's part of the tact of the job to try and identify when there are magic casts and use it for those, and on GNB to prioritise Camouflage for physical damage.