I can't imagine they are tbh
It depends on how you play them. They're low AC and low HP, so by high level (lets say 15) you're probably going to one-shot them. This isn't particularly a problem if they're played smartly. Throw in a couple Orc Warchiefs, a couple Eye of Grummush(sp). If the orcs need to rally an army to take down the players, play it like an organized fighting force. Flank. Stay at range when you can. Swarm. Keep commanders in the back where they can command. Separate the party.
Sure, evey round you'll lose X orcs where X is the number of attacks your party has per turn, but honestly if you're throwing a 100+orc force against the party, the goal isn't to have a one-on-one honorable combat with each player. It's to wear them out, drain their resources and overwhelm them into defeat.
Lets take the Orc War Chief "Battle Cry" ability:
First: it affects every
creature within 30 feet. It is clearly designed to be used with non-orcs in the war-party. Maybe ogres, trolls or some other beasts.
-Subpont: 30x30 is 36 squares, discounting the one square for the Orc War Chief, this is a maximum of 35 orcs.
Second: these 35 creatures then all gain advantage until the Orc War Chief's next turn. Advantage is powerful stuff.
Combine this with strategically keeping some units at range, with potentially 2 or three groups of these? That's over 100 attacks per turn, with
advantage. Even if the orcs are all at range and use their weaker javelin attack (1d6+3) that's ~100d6+300 dmg per round. Assuming half hit and average damage? +/-300dmg per round.
Also: fight on familiar terrain. Lure the players into a canyon, or a trapped plain. Don't attack the player's fortress, or if you do: do it the same way the players brought down the orc fortress, with careful planning and strategy.