Honest question, didn't the Yamamoto claim that no shinigami has been born stronger than him? If thats the case then are the 0th squad still weaker than him or was he not counting them?
Each member of 0 seems to be former Captains who have been promoted, so i do think he was counting them.

But just because old man Genocide might have been able to take any 1 member of 0 in a 1 vs 1 fight, and most of them in a 1 vs 2, then it doesnt mean he could have defeated them in a 1 vs 5.