Good points.
I agree with Sonny's temper being a failing. I would say though that the killing of Bruno Tattaglia was not so much for Michael getting punched but for the second attempt on their father's life.

Sonny was not a strategic thinker (as he freely admitted in the book) and perhaps that is where Tom "failed" him. Could Tom have given orders to Sonny's crew that Sonny is never to be allowed off the property? Or could Tom have arranged for Lucy to be moved closer to the compound? Dunno.

Getting Michael involved was not good but it was the only way they had at that time to eliminate a direct threat to Vito's life and make it clear to the other Families that the Corleones were still open for business. Maybe they could have waited but that's where rational thinking goes out the window. Since Sonny, Mike and Tom were Vito's sons, they weren't dispassionate about protecting Vito.

There was another link that someone posted that compared the Corleones to the United States politically. I won't repeat all of that but Sonny's primary failings were that he took things as he saw them and overestimated the ability of violence to attain goals. Basically Sonny is all id.