[Norfleet]

That's because you're allowing them to be caught one at a time, in the open. Don't do that. Use your armies to make feint attacks, attack in multiple places at once (with the expectation that you probably WILL lose one), and conceal kill teams in your regular forces. Standard armies retain a vital role throughout all periods of the game, but that role changes. In the beginning, it they may serve as the ridgecrest of your forces, but as the game advances, their composition must be altered to suit the changing face of the game: They need to become more mobile, yet more expendable.