Man of Steel Superman has a Mach 843 feat under his belt with reflexes to match per the guidebook. Remeber when he blitzed the warlord? Caught a grenade? Weaved through skyscrapers at hundreds of miles per hour?
He has always been at this level. It's just that he only had serious fights with his peers (Zod, Faora, Nam-Ek, Doomsday) before justice league. He has never laid a hand on fodder and this film was his first opportunity to face off against foes that were not his peers. He only looks faster and stronger because everyone else (except Flash) is slower and weaker. Zod would have wrecked Steppenwolf the same way Kal did.