Regarding DD, despite what some may believe, he wss not fired because he over spent or depleted the farm. In both those areas he did exactly what Henry wanted him to do.
The reason DD was fired was because he could not align himself with Boston's corporate culture of collegial management. Remember they almost fired him right after the 2018 season as we later learned. Dombrowski was fired because he did not involve his subordinates into his decision making process. And this was anathema to the internal workings of the Red Sox organization.