re: So if Alabama 'murderball' is the best way to win, why did they get away from it?

Going either pass or run dominant is actually a double-edged sword.
Heavy passing teams are more finesse oriented, while run offenses are more physical. That's ok for a while IF you've got the offensive talent to blow other teams away, but your practices being finesse and timing lose the physical aspect for the defense. In a couple of seasons you'll usually see the defense lose some of its effectiveness because they aren't challenged in practice, and get pushed around by some of the better teams on their schedule.
Moderation is the key to the success for the entire team.