Nice analysis here, but I'm inclined to think that Michael is actually superior to Vito -- that is, a better Don -- in this respect, and there is little doubt that Puzo would agree. Speaking of Sonny in the novel, Puzo writes, "He showed a merciless ruthlessness, the lack of which had been Don Corleone's only fault as a conqueror" (p. 222).
Well, who's superior is based on what is the measurement you choose.
On business terms Micheal was superior. Not only because he expanded the Corleone family business but his ruthlessness when it's necessary to kill.
And on family terms, Vito was superior. Micheal was foolish enough to make himself believe that what he did was for the good of the family.
