I honestly think that has more to do with the really weird thing where male Seekers are always identified by full names even though the "surname" is largely superfluous outside of immediate tribal dealings. It probably made more sense in the original Japanese thanks to their rigid adherence to honorifics. It's more relaxed lately thanks to Krile calling him "Raha" and core Scions lately dropping the "Tia" in dialogue, but I think that's Japanese familiarity rules at play again.

Also, you'd think they'd at least make sure Seekers won't call other Seekers "Mr. Tia," but it happens at least once per patch cycle.