And if they got a breakout offensive, the allies would have produced another million tanks. In civ terms, the game was over before Poland, if you want to find out why the allies won you have to figure out why the US had all those good production cities cranking out tech and troops when the Germans didn't even have a decent tile with oil.
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And yes, tactics are ultimately secondary to production. That doesn't change the fact that the Romans had to fight the Gauls while outnumbered in Battle of Alesia or Carthage's Battle of Cannae.
These sorts of events aren't really going to happen in Civ4. The tactical engine and decision making in Civ4 is just too shallow to have something like that ever occur.
So Carthage were going to lose against the superior Roman production eventually. That doesn't make Hannibal's win at the Battle of Cannae any less interesting.
Combat plays a strong role in all Civ games. Not least of which because of barbarians forcing you to defend yourself (which are impossible to diplomacy with).
You're going to be spending a non-negligible amount of time in any Civ game (from 2 through 6) building up a standing army, even if only for defensive purposes. Ideally, that aspect of the game should be fun.