I don't think Michael was a step down. He was a different kind of leader than Vito. Sonny would have been a step down...
Well lets put it this way he was a step up from sonny but a step down from vito
Still disagree.
Well, that's a different topic altogether: Whether or not Vito was a superior Don than Michael. I personally feel that he was, but that's an entirely subjective opinion. There's really no right or wrong answer. They're fictional characters. All you can do is agree to disagree.
I don't read anything into Tessio "not doing anything" when his crew got chased from the hospital. It was 1945, no one had cell phones for God's sake!
It's entirely plausible that Tessio would have called Sonny five minutes after Michael did. Plus, Tessio was so instrumental in the planning of the Sollozzo-McCluskey murders, I can't imagine that he was "one the fence" from way back then.
I think that Tessio came up with a contingency plan while Michael was serving his apprenticeship to Vito. When Vito died he made the more practical choice. Of course it was the wrong choice, but who would have bet on Michael from the outset? 
