The anime only covered upto old Testament novels(it is a bad adaptation,read the light Novels).
This powerspike happened in the New Testament Novels, which the anime haven't reached yet.New strong characters are introduced, Accelerator is becoming stronger,Touma is slowly reaching his true self, especially the Invisible Thing inside his right arm,and becoming multiverse level character.
You know that Meliodas,DK & SD can't exist in the world for long and causes calamities,but in this series there are many characters whose very presence will destroy the world,would accidentally destroy the world by moving an arm or a leg since they are too big of an existence for the world.