That's a good point, Olivant.
Vito probably could've walked away and quietly lived out his days after the attempt on his life, a la Frank Costello, after the Genovese-Gigante attempt on his.
However, it's all moot, because Sonny was too steeped in the business and far too violent and hell bent on revenge by nature, for this to have ever played out as such.
As far as legitimacy as a means to an end, I agree. Senator Corleone, governor Corleone....
American politics are the ultimate power trip, that's what Vito had in mind.