It seems like anybody can either be born with the echo (us, minfilia, others) or given it somehow via the Sahagin priest method. It's not just mutually exclusive to Hydelines power; I think the Echo is simply an ability that opens up possibilities the more you use it. For one, it connects us to Hydeline, for others it gives them body switching abilities.

With that said, us being the "champion of hydaeline" means she favors us more than any of the other echo users, probably because we're actually strong enough to beat a primal unlike the others.

Though I think primals sucking up her aether +her having to boost our anti-tempering abilites constantly weakens to the point where speaking is too much effort