Strategy for Blessings?

With another water blessing available as a reward and a new legendary hero on her way tomorrow, I am wondering about the best long term investment of the blessings. Because they are so rare and apparently can never be removed, it seems important to have some kind of strategy. How are you planning to use them?

For myself:

Originally I was thinking to pick units that work well with the legendary hero. I put my first on Bridal Cordelia: Mine has neutral IVs, so she makes good use of the +3 speed, and Fjorm likes her ask/spd rally when she's taking a defensive position. I was planning to give my second to Arvis, as he also benefits from the speed boost, and another poster pointed out that his built in defense and attack ploys work nicely with Fjorm's role as distant counter bait (although I guess arguably the attack ploy takes away from Ice Mirror's revenge damage).

HOWEVER - I am wondering if that is squandering the blessings because Cordelia and Arvis have such low BST, they will really never be viable in the top tier Arena. I'm imagining that we will see the legendary heroes a fair amount on the bonus units list, and thinking that maybe it makes more sense to tack the blessings onto high BST arena units to boost their score even further. Fjorm has OK BST and if she's entering the arena with three blessed allies, I think that could make a significant boost in the scoring (is that true?).

How do others plan on using the blessings?