Unlike 1e-3e, there is nothing inherent in the 4e rules to invalidate the use of traditional mass armies in the game world. Where 1e 0th-level men at arms and 3e 1st level warriors were utterly useless against even mid-level PCs, the power disparity in 4e is much less.
One thing I love in 4e is high level minions, who can represent well-trained but non-heroic troops. They can threaten even high level PCs, without presenting an unstoppable juggernaut to low level NPCs.
Eg: compare the Orc Warrior (9th level Minion) to the Human Rabble (minion) and Human Guard (3rd level soldier). Those orcs' high +14 to attack makes large numbers of them scary to PCs up into paragon tier, but yet their lowish AC 21 and 1 hp means that a squad of human guards could kill many of them, and even human rabble can threaten them.
You can do the same in reverse, eg create 10th level minion human Elite Pikemen based off the Human Guard, they can threaten PCs but low-level Orc Berserkers could plough through a bunch of them before going down. The 9th level human pirate in the MM2 is a particularly good candidate for minionisation IMO.
Anyway, yes, for the first time in D&D, mass armies are militarily valid. To me that is a great thing. Sure Epic tier PCs could dispatch hundreds or thousands of Heroic-level foes, but that's perfectly in-genre. You don't get the 3e situation where one PC with a 5th level fireball wand can wipe out the Duke's army singlehanded.
One thing I love in 4e is high level minions, who can represent well-trained but non-heroic troops. They can threaten even high level PCs, without presenting an unstoppable juggernaut to low level NPCs.
Eg: compare the Orc Warrior (9th level Minion) to the Human Rabble (minion) and Human Guard (3rd level soldier). Those orcs' high +14 to attack makes large numbers of them scary to PCs up into paragon tier, but yet their lowish AC 21 and 1 hp means that a squad of human guards could kill many of them, and even human rabble can threaten them.
You can do the same in reverse, eg create 10th level minion human Elite Pikemen based off the Human Guard, they can threaten PCs but low-level Orc Berserkers could plough through a bunch of them before going down. The 9th level human pirate in the MM2 is a particularly good candidate for minionisation IMO.

Anyway, yes, for the first time in D&D, mass armies are militarily valid. To me that is a great thing. Sure Epic tier PCs could dispatch hundreds or thousands of Heroic-level foes, but that's perfectly in-genre. You don't get the 3e situation where one PC with a 5th level fireball wand can wipe out the Duke's army singlehanded.