Even in regular DC lore Steppenwolf is not an alpha threat. The movie version kind of combine Steppenwolf with Kalibak, as he was made to be more powerful and was desperately seeking Darkseid’s approval. From their battles, it’s possible Wonder Woman could have taken Steppenwolf out solo in a fair one on one. He played a similar role to Loki in the first Avengers. Sure he was an Asgardian but Hulk totally embarrassed him. The point is that these villains are just the tip of the iceberg.
My problem with Snyder making Superman OP compared to the rest of the League is that it’s just a set up for his heel turn. Yeah it gives Supes a cool scene but in actuality it’s just a way to make him more scary and a bigger challenge for Batman to overcome. Cool entrance but you’re really just a plot device to make the real hero look better.