When Auron gave Tidus the sword, I bet he wasn't thinking about his old man. He was thinking "why couldn't you have given me a Blitzball instead?" Everyone knows they make the best weaponsOh I know, I agree. Give me something to defend myself with, I don't care what it is or whose it was
Maybe it had to be Jecht's sword to intrigue Tidus. "oh hey, here I am with a sword from this guy you haven't seen in years and let's fight all these monsters and oh would you like to know more?"
I just met you, and this is crazy, but here's your father's sword, fight with me, maybe?