Napoleon was able to win the way he did because social conditions in France permitted him to conscript as many soldiers as he wanted and basically usurp the entire economic output of the country for the war effort. He famously bragged to one opponent that he couldn't be stopped because he could afford to "spend 30,000 lives a month." Other European societies at the time hadn't yet conceived of making war that way. And, once they all finally got around to it, we ended up with World War 1.
Julius Caesar was the other major outlier but Rome was undoubtedly more technologically and socially "advanced" than the Celts he fought early in his career. Furthermore, basically everything we know about Julius Caesar's exploits comes from books written by... Julius Caesar. Surely, he had an incentive to make his victories sound as dramatic as possible.