Thanks for the reply!
Due to how Bound Beneath Indomitable Will is worded though, I'm not sure how big a benefit it is? Since it works on a per-model basis rather than a per-unit basis like Deathless Spirits.
With Deathless Spirits, when a model from a unit wholly within 12" is allocated a wound, you get to try to save it.
With BBIW, the model itself needs to be within 12" to get the extra save, so practically speaking it still needs to be close to a Hero.
Maybe that is a bigger deal than I rate it, but it seems pretty insignificant considering the requirements to get it.