No I actually like the 10%->10% idea, for two reasons:

* It puts the onus onto using it as a support-tool, not for ourselves. Beyond helped to break TBN, it'd be a wash for ourselves. And that's fine, rather buff TBN because of how unique that is.
* Rather, it's very strong when used on somebody else. Our HP pool is bigger, and it'd be 10% of our HP.

Plus, we can already use TBN on someone else. Meaning that'd be someone who can seriously shield others as needed, and that'd be a neat niche at least. And if nothing else we can keep using it on the other tank, while we slowly re-heal from the 1-2-3 combo.