Starfield, ED, SC do have many overlapping features. Such as the still unfinished Squadron 42 story campaign, walking inside spaceships, ship customization, exploring and interacting with NPCs in scifi cities, FPS and space combat, flight models, aliens, POIs on planets, space travel in star systems. So Starfield will deliver on numerous things which are lackluster or non-existent in SC and ED. They are competitors even though Starfield is not a (heavy) simulation, but a space themed RPG.
People say few would walk in one direction for 40 minutes to reach the zone boundary. That's true, because it's a waste of time on foot. However, they would do so with vehicles. Bethesda did not add atmospheric flight because it's difficult to develop and players would feel the artificial limitations of the zone in a few minutes. ED and SC are far superior in this regard. It's about the freedom of exploration to get into your ship, manually control it, fly anywhere across a planet, land anywhere, discover POIs or just enjoy the vista. That is in my opinion critical for the ultimate immersive space sim.