Erdrick has taken on a lot of monsters over the years. As a result it’s fair to say that he knows his own limits better than anyone. That’s why he will know right away that he can’t handle an opponent like Phoenix Ikki. Ikki can slay most monsters in an instant and by the same token even Erdrick won’t be able to do anything. His shield would be absolutely shattered in a battle and I don’t see his sword being able to scratch Ikki’s armor. With no viable attack option at the ready that means Erdrick is doomed here. Phoenix Ikki wins.