I think you're referring to when Meliodas said he created the sins to defeat the commandments. He meant now. It was him glauximia, drole, and a member of the goddess race that fought 3000 years ago. Also king MAY have been alive but he would have been way too young and way to weak.
There weren't any others, meliodas created the sins and they all just came together I believe, and the SDS were NOT around 3000 years ago, they were made when meliodas became a holy knight. ( I haven't seen SDS in a while, but I finished the manga and I'm almost sure I'm right)
Meliodas never showed his true personal magic ability, making him stronger than Escanor at high noon. In the story, he says if he were to show his true magic, he wouldn’t be able to live there anymore.