If I remember the story correctly, Achilles is killed in the Iliad. By the time the Odyssey starts, he’s already dead and the only appearance he makes in that book is as a ghost for a few lines. If Nolan follows Homer, who cares who plays his ghost? It’s not like Ellen Page is going to be riding a chariot battling Hector.
If Page plays Achilles as a ghost, they can make her as tall as they want, and add some muscles.