Are Deathstroke and Luthor Collaborating?? IMO they would individually prep as they are rather independent characters. If they don't collaborate they lose easy if they plan together they may pull as much as a 6/10 win rate. Luthor as intelligent as he is overcomplicates everything and he lacks the know how in direct confrontation that DS and Kang have. However if he outfits DS and DS tells him when he's overcomplicating his crap and keeps his Luthor gear practical team has a chance.
Like I said I think it comes down if DS and Lex are actually working "together" or are actually putting their heads together in one effort rather than each of them putting together their own plots and attacking at the same time.