Because Arwen could not have ridden against the 9, at all. They could have replaced Glorfindel or removed him, i understand, but the powers he had came from ha

Because Arwen could not have ridden against the 9, at all. They could have replaced Glorfindel or removed him, i understand, but the powers he had came from having lived over the sea. Arwen was born in Middle Earth and simply could not do what was attributed to her in the films. (It is the earliest lore incompatible change that springs to mind)