Here's how to fix TBN

[Crater]

We want the shield to break, additional mitigation on top of it would make it harder to do so.

If you're in a situation where TBN is "hard to break" then you're in a situation where you don't need, and probably shouldn't be using, any defensives in the first place, because your healer is basically going to keep you topped off just by doing DPS and is going to be overhealing you by the time they take care of the mandatory partywide healing they have to do to keep the DPS alive from unavoidable damage. That scenario has zero relevance to anything.