When they rewrote Justice League, Darkseid mostly was going to be saved for the second part, BUT he was going to appear in the first part when Diana tells the story (it also wasn't going to be a voiceover infodump but the start of the film) of the prior Apokolips invasion. It wasn't going to be Steppenwolf who came before, it was going to be Darkseid himself who was beaten back. Steppenwolf's plotline was that he was coming this time to try and gather the mother boxes to restore his place in the eyes of Darkseid as he had fallen out of favor and thus open the way for Darkseid to come and acquire the Anti-Life Equation.
In the theatrical cut, Steppenwolf still has like a single line left about how this is why he's even in the film. A ton of his dialogue was cut out because that plotline was excised and that's why the Justice League has to spend so much time standing around and explaining what the plot is. (A bunch of those scenes were added by Whedon, you can tell by if Wonder Woman is not in the shot with anyone else, Gal Godot couldn't shoot her scenes with the rest.) Then they stuck Steppenwolf back in the prior invasion so he seemed more dangerous and powerful and stuff rather than just being a Darkseid lackey since Darkseid was excised from the film too.
BvS suffers in the theatrical cut for similar reasons as Clark's plotline, and parts of Lois' got sliced out. That's why the Ultimate Cut seems shorter despite adding 30 minutes, there's a clear build up of events for all the characters, with Luthor at the center of it. You actually see Clark and Lois investigating and uncovering the plot, you see Clark investigating Batman and realizing that he's become dangerous too, etc. It doesn't just jump to Luthor suddenly telling them to fight, you're shown how he's manipulated everyone.
Also amusingly, Luthor's craziness is explained better in the Ultimate Cut, as the scene where he talks with Batman in his cell is extended. He explains his constant crazed obsession with gods and everything in the film is due to having been told by the Kryptonian ship about Darkseid, and that he essentially was planning everything in order to eliminate what would attract Darkseid back to Earth: Superman. Except they've screwed up, there's more superheroes, there's mother boxes on Earth, it now doesn't matter, Darkseid is coming anyway.
And he's a god.