Satan coming out of seclusion was indeed because he'd already cultivated himself to the peak of the Legendary Realm.
In theory, the Legendary Realm was without limits; even if there was no way to become a demigod, you could still grow stronger at an unceasing pace, continuously becoming more and more powerful.
Such Legendary Masters had existed back in relatively more savage, ancient times. Their formidable level was such that it was even enough to shock the gods—forget weak Divine Power, even if you had low-level Divine Powers, it wouldn't necessarily be enough to compete with them.
But legendary was still legendary. If you hadn't truly completed your life's transformation, that meant you hadn't escaped the river of time and had ignored the ability available to you as it passed you by. Following the passage of time, these impossibly powerful Legendary Masters were ultimately unable to defeat time itself, each of them growing older and dying instead.
