Whatever arc Perez envisioned for Steve would have also reached an endpoint. Just about any longrunning character from the Big 2 has this issue, which is why we get so many repeated plots.Like Largo said, anything can be done with them. Perez created a Steve who was pretty much done as a character, he was a grown man who joined the military as a hot head then matured as he got a front row seat of how devastating war can be. Why didn't he start Steve out as young so we could actually see that growth process? Have him and Diana get into philosophical debates on war and peace, it would give them a relationship that challenges them both intellectually. Writers could toy with them switching positions on which one is the hawk and which one is the dove depending on the story. Or tackle themes of toxic masculinity and contradictions in Steve's psyche. He joined the military because he thought guns were macho, what lessons does he learn from interacting with Diana and the Amazons, and how does it mesh with being inspired by his mother?
Etta should be a mix of Lois and Jimmy. Lois is an inspiration to women, but she's also conventionally gorgeous. Etta is a different type of beautiful that can be inspiring in a different way, and she's a weirdness magnet like Jimmy. Etta was able to carry at least one Golden Age story on her own, and she was considered a highlight in LoWW where she had her own life and dynamics at Holliday College, including a rivalry with a resident Alpha Bitch. She is the same age as Diana, so she's filling a role as a true peer that neither Julia or Vanessa can really fill. She's a young independent woman who is navigating Man's World on her own for the first time. She's lived here all her life while Diana is a stranger. How do their experiences differ, and what similarities are there? And the Holliday Girls are pseudo Amazons. How does Diana react to their community of women, who come together to support each other within man's world and without the magical safe space the Amazons have where man's influence and abuse can't touch them? College campuses are not safe for young women after all.
The arcs you mentioned for Julia and Vanessa were great. But they are also all said and done. In the old continuity, Julia reconciled with Diana and Vanessa was cured, and being dragged back into further adventures wouldn't be good for her. They were great characters, but they reached a natural end point. Bringing them back in Rebirth had proved to be a disaster. What can be said about them that hasn't been said already?