but the npc origin characters never have the qualifications to be a true savior.
Clearly they do have the qualifications because they CAN be the hero...and again, no canon, every possible ending with every possible character that reaches that ending whether origin character or not is equally valid. There is no pre-defined canon assigned "true savior"...any character the player can play could be the savior, or the worst villain of the story or anything in between and they are ALL equally valid. There are no such things as "true" anything in this game, not unless Larian officially declares certain possibilities to be canon, but they haven't and they probably never will...because that's the beauty of choice here. Also even if they were to eventually declare a "canon" it would be wise not to assume the best good aligned ending must be it...there have been other games in the past that declared bad endings or even failed states as the "canon" for their sequels...so whatever mega heroic best ending you might have had in the previous game didn't count for anything canonically.
we can see the origin characters are "advanced mode". if we play them as the player character, they will have more difficult paths, because of their deadlock backgrounds.
yes, they should be able to find the true path, because your soul is in their bodies.
but still, they will have the limitation, because of the deadlocks. and will be leaded to the bad ends easy because of the deadlocks.
such as a sorcerer tav can gain mystra's love easily. but this is impossible for gale, somethings pass can not return again.
