I am deeply convinced that when playing Humans against the Elves, one should never focus on retraining units in a one-sided manner. In other words, if you convert all armored infantry into monks, I will become a sworn enemy of the monks, which will include most of the armored infantry. Thus, the Vengeance skill kills two birds with one stone (both monks and armored infantry that have become monks). Therefore, it is better to train archers, armored infantry, monks, and cavalry... This advice applies only to battles against the Elves.