Beorn's impact on the Battle of 5 Armies is to scatter the Bodyguard of Bolg and then to 'crush' Bolg himself. It is at this moment that the Goblin army goes limp at the knees and want to cash in their return tickets back to the Misty Mountains. (presumably travelling by Warg Express?) I just love the phrase
(When the Chief warg gets a burnt nose all order is lost in the glade. But that is a poor example of this trend)Dismay fell on the Goblins
In Moria the death of the Frodo-spearing Black Uruk captain gives the fellowship a lull in proceedings and the chance to escape.
.His followers fled howling
And the death of the Witch King halts the attack on Minas Tirith. If there had not been the Easterlings and the Haradrim (plus mumakil) to rally behind I suspect that the orcs of that army would not have hung around either.
The removal of the Will of Sauron leaves the Mordor forces without any will or direction to fight the Captains of the West at Cormallen. (that's when Sauron sees what's happening over at Mount Doom and gets a bit distracted..)
In conclusion, the Forces of Sauron do not have anything like the free will of their enemies to simply take over command in a crisis. Nor do orcs have much of a sense of duty unless compelled or driven.
My point being that I think that taking out the leader of the opposition should have a major impact on a bunch of Orcs and/or Goblins being faced by a fellowship. Reducing all Orc Hate levels to 1 point each perhaps or forcing them into a collective Fear check of their own based on the highest attribute amongst the remaining adversaries?