Alright so Zamasu said that he (or he and Black, whatever) killed all of the other Gods in their timeline. Are we supposed to believe that either of them are capable of killing Beerus? Because I dont.
Furthermore, they would have had to have exterminated all of their timeline's Gods before Black's trip to the "current time" when he chased Trunks' time machine through the time rift. Goku beat his ass as just regular SSJ. Theres no way that Black could have beaten Beerus before gaining SSJ Rose (or even after he gained it, in my opinion).
They briefly talked about how Whis, like other attendants, go dormant when their God is killed, which would imply that this is the case.
I have a hard time believing that even Zamasu/Black fusion could take down Beerus, let alone them on their own, let alone back when Black was weaker than SSJ Goku.
I like DBSuper but it definitely contradicts itself sometimes.