-Only read first post-
I can't say for sure, but I think Capcom simply wanted to make Sparda a total god, so they gave him the Yamoto, but simply for the reasons of giving Sparda absolute power, it turned into the Sparda itself wen he devil triggered.
As for why Arkaham couldn't turn Force Edge into Sparda, I'm guessing Sparda has some sort of spell or something on it to stop it from being weld by anyone outside his bloodline.
@Wildfire-Lol, this his no signifagance to anything, just saying, Vergil's amulet is on a black chain in DMC1
*Been here over two year ^_^*
I ain't back for real..... But rest assured, I'm still watching over this place.