I think the main reason Micheal wasnt a good of a Don as many say he shoulda been was that he was undereducated and lack of experience. He wasn't taught skills or anything and he didnt know much about the family business. As for vito he developed the skills out of necessity. He needed to do the things in order to survive. And im sure he had mentor's and ppl to learn from.. All micheal had was Vito and Tommasino which he was limited in both. Everyone else in the family didnt have much experience. Sonny dead, tessio dead, Clemenza started own family then died. Basically he only had Tom who was only Consiglieri for a breif amount of time