Before Prime had even taken his 15,000 year-long sundip, he had already been amped by the Source itself(ie. "powers gleaned from the very edge of time and space"😉, and was essentially acting as the battery for the entire Superman Lineage -- granting them with powers "far beyond any held by any metahuman ever."
S1M is essentially the Surfer to Prime's Galactus. This is a stomp of epic proportions.