Michael would've made a good wartime Consigliere...Maybe one who could've gotten through to Sonny's hot temper.
Imagine a team with Sonny as Don, Michael as Consigliere....I think it could've worked.
I think Sonny would of been better as Michael's underboss, his temper would keep the troops in line and if Michael handed down a hit order Sonny'd be best to carry it out, that being said though I don't think the baptism hit would of went down as well if Sonny was around.