I disagree, I think it's to set up Yelena up as the second Black Widow. They're setting young avengers! It's one of the reasons why Cassie Lang was in Endgame (one of the two times that movie made me cry.) As well as Harley Keener from IM3. Young Avengers are gonna be Cassie, Yelena, Kate Bishop from the hawkeye series, Harley, Speed who will be introduced in Wandavision and someone else that will be introduced in the film.