maining dark or light is great, but if you do decide to make the satan + osiris combo your main account, your other problem would be that there's not gonna be a free dark event eidolon until september (Trivia) for your dark team (unless you get or reroll another dark combo w/ an SSR gacha dark eido, then you won't have any problems I guess)
If you decide to go light, you won't have to wait long for an event light eido since baron event is coming close