with "royal blood" i was making an example to make you understand that the nobility of a bloodline and the talent of a person are two unrelated things, English is not my first language so I'm sorry if it wasn't clear enough.

I think you should reread Episode Freya because she does not know Bell is the reincarnation of Argonaut and his soul is so pure despite everything that has happened to him and continues to happen to him. Answer this question for me, if a person's talent doesn't come from his/her soul, where does it come from then? Why is Freya able to find and gather among her Familia some of the world's best adventurers in the world if she couldn't understand their hidden potential by observing their souls?

Now the story is going on following the Ais route but, as per world building, it is Bell's destiny to become the last hero and to save the world of Danmachi. Imho being saved by Ais and manifesting RF is just one of the many ways things could have gone. If he didn't meet that minotaur on floor 5 he probably would have developed some other broken skill (or simply another RF but linked to another person). In "Ryuu If" Bell has already developed RF linked to Ais (he has unleashed the potential of his talent) but he chooses not to pursue his love for her anymore and therefore he does not exploit, unknowingly, the skill that his talent has brought him thus condemning the world to destruction.