You're advocating a blitz strategy which in all Total War games is always the optimal and easiest way to beat the AI with. Its nothing new and for some crazyass players they could conquer the entire map in M2:TW in like 20-25 turns, course beating the AI before they develop is like clubbing baby seals. Fun for the first time then gets really boring since you're racing out so far ahead that you dont get to use any high tech units.