Actually, the team's record is the measuring stick for all MLB managers. You win, you stay. You lose, you're gone. You can also be gone when you win if the FO thinks the team under performed. Managers are hired to be fired, and I frankly think that's fair.
As for Cora, he has been quite different from Farrell, so it's hard not to give him credit because almost all the same guys are back this year. JD is the one real addition, and one guy can't do it all, nor has he. Plus, as moonslav reminds us, the players aren't playing hurt this year. Bogie and Pedey are on the DL and that hasn't seemed to hurt.
The Sox have the best record and the the best run differential in MLB. The players did that, but Cora sure as heck hasn't hurt and probably has helped.