For elo survivor
SOA is needed
i tend to pack my decks with them to combat vs Pill manipulation which can ruin your streaks because once they have that pill disadvantage from the start they can control the game
mono is recommended in elo survivor as is a semi mono deck (6-1-1 splits for example).
examples include rescue who i have seen get high records in this game type and are frequently used in the game type.
however half decks are just as good and will help counter weaknesses lets not forget.
even 4-3-1 splits are still relatively strong in this game type.
so there is a choice with survivor elo
mono - means you always have that ever so important clan bonus in your hand at all times but it might become a struggle vs weaknesses and can guarantee a loss.
dual deck - means you can cover weakness and not have to rely on some dodgy choices for your mono deck however you can experience poor 3-1 splits that can ruin you as the bonus is quite important in elo survivor for the win streak.