True, in the deleted scene he counsels Sonny to wait and consult with Vito. But after the hospital he changes his tune fast. Michael realizes that Santino was not wrong at all. He sides with Sonny over Tom by supporting (and committing) Sollozzo's murder.

Michael and Sonny are more alike than most realize. Michael's thinking is every bit as aggressive as Sonny's, but Michael adds a cerebral, strategic dimension that Sonny lacks.

I don't consider Michael "slow and steady" at all. He moves boldly and forcefully once he has identified a goal or an enemy.