I wouldn't hand them Devoted Spirit because it's not appropriate to this class as I see it. If I perceived the fluff as more Soul Disciple-esque, I would do it hands down.

A solution along those lines pigeonholes races even more than they're supposed to be pigeonholed. One of the reasons substitution levels exist is so that you, the player, can make a choice to fit into your race's archetypes. If every Soul Blade has a discipline based on their race, every Soul Blade is pigeonholed by their race.

And I'm still not seeing how giving disciplines by race has anything to do with this class or its concept. The Soul Blade is a tough guy who fuses spiritual energy with his sword. That's about it!