Batman is human, there’s nothing more to it. In a match of strength, Darkseid would be unstoppable. Even considering Batman’s arsenal of technology, he would be overcome by the New God, whose tech is far superior to any on Earth. Where the challenge would become interesting is between two strategists.
Darkseid is a wartime dictator and a conqueror on an intergalactic scale, a role one can’t come by on brute power alone. Bruce Wayne would challenge Darkseid as an equal thinker, making any fight between the two more of a chess game than a fistfight. As is often the case, Bruce could take a leadership role among the League in the film in order to orchestrate a plan to best utilize each hero’s strengths.
Much like Batman, Cyborg relies on technology as a hero. But unlike the other heroes, Cyborg is the technology. As his moniker implies, Victor Stone’s body is mostly machine with little besides his mind remaining “human.” Such a dependence on Earth technology would create a weakness against the Apokaliptian overlord, as New Gods are (literally) the most technologically advanced group in the DC universe.
But Cyborg’s origins offer him a secret weapon against Darkseid. All of Victor’s cybernetic enhancements are infused with the energy of New God technology (because new god tech was responsible for Victor needing the cybernetics in the first place). Not only does this give the hero an advantage, it offers the film a simple way to set up its plot.
Cyborg is able to tap into New Gods’ data and digital stores, potentially revealing Darkseid’s initial invasion plan – this is the exact scenario that spurred the events of the Justice League reboot for the New 52. Cyborg essentially has the power to operate on the same technological level as the New Gods making him an invaluable asset to the team.
Like Superman and Wonder Woman, Aquaman has super strength that can help him hold his own if it comes to fists with Darkseid. But Aquaman is (please excuse the pun, I couldn’t resist) a fish out of water on Apokalips. Aquaman has numerous powers related to the seas he rules over, but none of them would come in handy unless Darkseid met the hero on his own turf.
But Aquaman will likely be one of Darkseid’s more intended targets if he attacks Earth. Arthur Curry is the King of Atlantis and by extension most (if not all) of the world’s oceans. He is a powerful ruler on par with Darkseid, though much more benevolent, making him prime prey for the New God’s conquest. It’s even possible that Aquaman would have something none of the other heroes have: Darkseid’s respect.